UC-NRLF 


B    M    DTI    725 


ATORY  MAN' 
MY  ZOOLOGY 


MEMCAL    SCHOOL 


A  LABORATORY  MANUAL  FOR 
ELEMENTARY  ZOOLOGY 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 


THE  BAKER  &  TAYLOR  COMPANY 

NEW  YORK 

THE  CAMBRIDGE  UNIVERSITY  PRESS 

LONDON 

THE  MARUZEN-KABUSHIKI-KAISHA 

TOKYO,  OSAKA,  KYOTO,  FTJKtJOKA,  8ENDAI 

THE  MISSION  BOOK  COMPANY 

SHANGHAI 


A   LABORATORY  MANUAL 

FOR 

ELEMENTARY  ZOOLOGY 


By 
L.  H.  yHYMAN 

Department  of  Zoology,  University  of  Chicago 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 


COPYRIGHT  1*19  BY 
THE  UNIVERSITY  or  CHICAGO 

All  Rights  Reserved 


Published  May  1919 

Second  Impression  December  1919 

Third  Impression  December  1921 

Fourth  Impression  January  1923 

Fifth  Impression  October  1923 

Sixth  Impression  October  1924 

Seventh  Impression  October  1925 


Composed  *md  Printed  By 

The  University  of  Chicago  Press 

Chicazo,  Illinois.  U.S.A. 


INTRODUCTORY  NOTE 

This  laboratory  manual  was  prepared  for  the  dass  in  elementary  zoology  in 
the  University  of  Chicago,  and  has  been  used  in  this  course  for  some  time.  In 
the  three  months'  time  allotted  for  the  course,  nearly  all  of  the  work  given  in 
sections  I  to  XII,  inclusive,  is  completed,  with  the  exception  of  the  muscular  and 
skeletal  systems  of  the  frog.  The  remaining  sections  have  been  added  for  pub- 
lication because  they  seem  to  the  author  to  be  essential  for  a  complete  course  in 
general  zoology.  The  directions  have  been  written  entirely  from  the  material, 
although,  of  course,  many  textbooks  have  been  consulted  throughout.  An 
attempt  has  been  made,  not  merely  to  give  explicit  directions  for  the  study  of  the 
material,  but  also  to  point  out  the  relation  of  each  section  of  the  work  to  the 
general  principles  of  biology  and  to  make  clear  why  each  particular  kind  of 
material  has  been  selected.  The  sections  are  given,  naturally,  in  the  order 
which  the  author  thinks  most  logical,  but  they  can  be  shifted  at  the  will  of  the 
instructor.  Our  experience,  extending  over  many  years  of  trial  of  both  methods, 
has  shown  that  starting  the  course  with  the  dissection  of  a  complex  animal  is 
much  more  satisfactory  than  introducing  the  student  at  the  start  to  the  lower 
invertebrates,  for  the  reason  that  the  simplicity  of  the  latter  cannot  be  appre- 
ciated and  understood  except  with  reference  to  completely  differentiated  animals. 
Any  vertebrate  would  serve  the  purpose,  but  the  arthropods  are  in  general  unsuit- 
able because  they  introduce  the  problem  of  heteronomous  segmentation  for  which 
the  beginner  is  not  prepared.  Many  teachers  will  object  that  the  instructions 
are  too  detailed  and  that  it  is  better  pedagogy  to  compel  the  student  to  work 
out  things  by  himself;  but  the  large  amount  of  ground  which  must  be  covered 
in  a  relatively  short  time  and  the  impossibility  of  providing  sufficient  laboratory 
assistants  for  the  large  classes  with  which  we  have  to  deal  necessitate  detailed 
directions.  The  student  pursuing  the  modern  college  curriculum  simply  does 
not  have  time  to  carry  out  an  original  investigation  on  the  anatomy  of  an  animal; 
and  unless  he  is  provided  with  detailed  directions,  instructors  and  assistants  are 
overburdened  with  the  task  of  explaining  to  him  what  he  is  looking  at,  what  to 
do  next,  etc.  There  is  no  reason  why  this  extra  work  cannot  be  avoided  by 
including  these  explanations  in  the  manual. 


GENERAL  DIRECTIONS 

1.  Obtain  from  the  cashier's  office  a  biology  breakage  ticket  ($5.00).     Take 
this  to  the  office  of  the  superintendent  of  buildings  and  grounds  (Room  2,  Press 
Building)  and  present  it  for  a  microscope.     Ask  for  a  compound  microscope  with 
high  and  low  objectives  and  oculars.     Rental  charge  for  the  microscope  will  be 
deducted  from  the  ticket.     Procure  a  padlock,  bring  your  microscope  to  the 
laboratory,  and  follow  4. 

2.  Deposit  your  breakage  ticket  with  the  storekeeper  in  Room  10,  Botany 
Building.     Supplies  needed  for  the  laboratory  are  obtained  from  this  storeroom, 
the  cost  is  checked  off  on  the  breakage  ticket,  and  the  unused  portion  of  the 
ticket  is  refunded  later. 

3.  Obtain  at  Room  10,  Botany  Building,  after  you  have  deposited  the 
breakage  ticket,  the  following  supplies: 

One  fine  scissors. 

Two  small  forceps  with  straight  points. 

One  medium-sized  scalpel. 

One  probe. 

Six  slides. 

Two  teasing  needles. 

One  dozen  square  cover  glasses. 

Three  medicine  droppers. 

One  tripod  hand  lens. 

A  paper  of  pins. 

A  towel. 

A  padlock. 

If  you  already  have  some  of  these  materials,  do  not,  of  course,  purchase 
new  ones. 

4.  Select  a  locker  in  the  laboratory  or  have  one  assigned  to  you  and  place 
your  padlock  on  the  door.    Keep  your  microscope,  instruments,  and  drawing 
materials  in  this  locker.     If  you  want  a  clothes  locker  in  the  hall,  buy  a  50  cent 
key  deposit  ticket  from  the  cashier's  office,  and  present  this  for  a  key  at  Room  2, 
Press  Building. 

5.  Purchase   the  following  drawing  materials   (University  Press  or  other 

bookstore) : 

Drawing  paper,  No.  6 — a  smooth,  stiff  paper  is  required. 

Note  paper,  No.  6. 

Notebook  cover,  No.  6. 

Hard  pencil,  6H. 

Eraser. 

Ruler. 

Pad  of  sandpaper  for  sharpening  the  pencil. 

vii 


GENERAL  DIRECTIONS 

6.  Books  referred  to  are  Holmes's  Biology  of  the  Frog  and  Hegner's  Introduc- 
tion to  Zoology.     Purchase  these  only  if  directed  by  the  instructor. 

7.  Select  a  place  in  the  laboratory  and  write  your  name  on  the  table  with  a 
piece  of  chalk  or  paste  a  gummed  label  with  your  name  on  the  table  at  the  place 
chosen. 

8.  Present  yourself  with  all  of  the  foregoing  materials  ready  for  work  at  the 
beginning  of  the  first  laboratory  period.    Do  not  handicap  yourself  at  the  start 
by  delaying  to  provide  yourself  with  the  necessary  outfit.    The  microscope  will 
not  be  needed  for  the  first  few  days. 

9.  A  box  of  slides  will  be  issued  to  each  student  later  in  the  course.     Examine 
them  to  see  that  none  are  broken  or  damaged.    These  slides  are  to  be  returned 
at  the  end  of  the  quarter,  and  a  charge  of  50  cents  will  be  made  for  each  broken 
or  injured  slide.     Students  are  requested  to  handle  the  slides  with  care. 

General  Instructions  Regarding  Drawings 

1.  All  drawings  must  be  made  on  good  quality  drawing  paper  with  a  hard 
pencil.    As  experience  has  shown  that  hard  pencil  drawings  are  the  most  satis- 
factory, no  other  kind  will  be  accepted. 

2.  All  drawings  must  be  made  from  the  actual  material,  unless  otherwise 
directed,  and  completed  in  the  laboratory.    The  making  of  rough  sketches  in 
the  laboratory  to  be  completed  elsewhere  is  unscientific,  inaccurate,  and  not 
permissible.    Drawings  copied  from  textbooks  will  not  be  accepted. 

3.  The  drawing  should  contain  all  structures  mentioned  in  the  outlines,  as 
only  those  readily  found  are  called  for.    In  case  you  cannot  find  any  structures 
mentioned,  ask  the  assistants  to  help  you.    Put  into  the  drawing  only  what  you 
have  actually  seen,  and  in  case  you  were  unable  to  find  certain  things  make  a 
note  to  that  effect  under  the  drawing. 

4.  The  prime  requisite  of  a  drawing  is  accuracy,  i.e.,  it  must  resemble  the 
actual  specimen  before  the  student  as  closely  as  possible.    Drawings  are  not 
to  be  diagrammatized  unless  the  outlines  expressly  direct  to  make  them  so. 
Next  to  accuracy,  neatness  and  good  arrangement  on  the  page  are  desirable. 

5.  Make  your  drawings  large  enough  to  show  dearly  all  details  asked  for; 
students  tend  to  make  drawings  too  small.    The  more  details  called  for,  the 
larger  the  drawing  must  be. 

6.  Always  keep  the  pencil  sharp  by  means  of  sandpaper. 

7.  Draw  on  one  face  of  the  page  only,  on  the  face  which  lies  to  your  right 
hand  with  your  notebook  open. 

8.  Label  fully.    Label  everything  in  the  drawing  regardless  of  whether  the 
same  structures  have  already  been  labeled  in  some  previous  drawing.     With  a 
ruler  draw  a  straight  line  out  from  the  object  to  be  labeled  and  write  or  print 
the  label  so  that  it  is  parallel  to  the  top  and  bottom  edges  of  the  page. 


GENERAL  DIRECTIONS  ix 

9.  Do  not  write  notes  on  the  drawings.    Write  them  on  separate  pages  and 
insert  them  next  to  the  drawings  to  which  they  refer. 

10.  Students  who  declare  that  they  "cannot  draw"  will  receive  little  sym- 
pathy.   Anyone  can  make  the  simple  line  drawings  required  hi  this  work.    To 
make  a  drawing  proceed  as  follows.    First  determine  how  large  it  is  to  be  and 
select  a  proper  space  on  the  page.    Then  rule  this  space  with  very  light  vertical 
and  horizontal  guide  lines  so  that  your  drawing  will  be  symmetrical.    With  a 
ruler  further  reduce  or  enlarge  the  length  or  width  of  the  actual  object  to  fit  the 
space  selected.    Then  with  very  light  lines  make  an  outline  of  the  object;  then, 
constantly  referring  to  the  object,  correct  this  with  light  lines  until  the  propor- 
tions and  details  are  as  nearly  like  the  object  as  you  can  possibly  get  them. 
Then  erase  the  light  lines  until  you  can  barely  see  them,  and  go  over  them  making 
the  final  lines  firm  and  clear.    Every  line  upon  the  drawing  must  represent  a 
structure  actually  present  on  the  object.    Avoid  shading,  color,  crosshatch- 
ing,  etc. 

Notes 

1.  Whenever  desirable,  notes  are  to  accompany  the  drawings  and  are  to  be 
written  on  separate  sheets  which  are  to  be  inserted  in  the  notebook  adjacent  to 
the  sheet  containing  the  drawings. 

2.  Avoid  detailed  notes  containing  material  in  the  laboratory  outlines. 

3.  The  notes  will  consist  of: 

a)  Answers  to  questions  contained  in  the  laboratory  outlines  unless  such 
questions  are  obviously  answered  in  the  drawings. 

b)  Additional  explanations,  original  observations,  or  comments  upon  any 
of  the  laboratory  work  as  the  student  sees  fit. 

c)  Complete  accounts  of  experiments  performed  in  the  laboratory,  whether 
individual  or  demonstration.    This  account  should  follow  some  such  plan  as 
this:  (i)  purpose  of  the  experiment,  (2)  observations  and  results,  (3)  conclusions 
and  explanations. 

4.  It  is  preferable  but  not  compulsory  that  the  notes  be  written  in  ink.    Write 
on  one  side  of  the  paper  only. 

) 

Additional  Miscellaneous  Directions 

1.  The  letter  (A)  signifies  consult  the  assistant;    (R),  consult  a  textbook; 
(Z,),  the  matter  will  probably  be  discussed  in  the  lectures. 

2.  Right  and  left  refer  to  the  animal,  not  to  the  student,  unless  so  stated. 

3.  All  work  is  to  be  individual  unless  the  supply  of  material  is  insufficient. 

4.  When  handling  small  living  animals  with  a  dropper  be  sure  that  the  dropper 
has  never  been  used  for  chemicals.     Have  one  dropper  plainly  marked  which 
you  use  only  for  water  or  other  harmless  solutions.     It  has  often  happened  that 


X  GENERAL  DIRECTIONS 

the  entire  supply  of  animals  for  the  class  has  been  killed  because  some  careless 
student  used  a  dropper  which  he  had  previously  employed  for  chemicals. 

5.  In  dropping  a  cover  glass  upon  a  slide,  first  put  one  edge  of  the  cover 
glass  against  the  slide  until  the  liquid  on  the  slide  comes  in  contact  with  the 
cover  glass,  then  lower  the  cover  glass  slowly.     In  this  way,  air  bubbles  under 
the  cover  glass  are  avoided. 

6.  Mount  living  animals  in  water.     The  water  should  be  sufficient  in  amount 
to  come  to  the  edges  of  the  cover  glass  but  not  enough  to  cause  the  cover  glass 
to  float  about.     Absorb  extra  water  with  a  piece  of  filter  paper.     While  examin- 
ing living  animals  be  careful  that  the  water  does  not  dry  up.     When  this  happens 
the  animals  will  begin  to  slow  down  their  movements,  to  flatten  out,  and  finally 
to  burst.    Replenish  the  water  from  time  to  time  by  placing  a  drop  in  contact 
with  the  edge  of  the  cover  glass. 

7.  Living  tissues  of  an  animal  must  be  mounted  in  fluid  of  the  same  osmotic 
pressure  as  the  fluids  of  the  animal.     In  the  case  of  the  frog,  this  is  a  .  6  per  cent 
solution  of  common  salt. 

8.  When  dissecting,  have  the  animal  firmly  fastened  to  the  wax  bottom  of  the 
dissecting  tray  with  pins.     Insert  the  pins  obliquely,  not  vertically,  so  that  they 
will  not  get  in  your  way.     Dissection  is  usually  to  be  carried  out  under  water. 
Dissect  with  blunt  instruments,  forceps,  or  probe,  and  have  an  instrument  in 
each  hand,  one  to  hold  the  part,  the  other  to  dissect  with.     Never  cut  anything 
unless  you  are  sure  what  you  are  cutting.     Dissect  lengthwise  along  blood 
vessels,  nerves,  tubes,  etc.,  not  across  them. 

9.  In  staining  tissues,  use  a  small  amount  of  the  stain.     If  the  stain  is  applied 
before  the  cover  glass  is  put  on,  drop  a  small  drop  of  the  stain  on  the  tissue,  then 
cover.    If  the  stain  is  applied  after  the  cover  glass  has  been  put  on,  place  a  drop 
of  the  stain  in  contact  with  one  edge  of  the  cover  glass,  apply  a  piece  of  filter 
paper  to  the  opposite  edge,  and  draw  the  stain  under  by  suction.     It  generally 
requires  a  few  minutes  for  a  stain  to  act,  especially  when  living  animals  are  to  be 
stained.     If  too  much  stain  is  used  the  whole  structure  becomes  uniformly 
stained,  so  that  the  details  are  blotted  out.     In  this  case,  make  a  new  prep- 
aration or  remove  the  excess  stain  by  running  a  little  dilute  acid  under  the 
cover  glass. 

The  Use  of  the  Microscope 

i.  Parts  of  the  microscope.  Remove  the  instrument  from  the  case.  It  con- 
sists of  a  horse  shoe-shaped  base  from  which  arises  a  vertical  pillar,  from  which 
extends  an  arm  supporting  a  vertical,  hollow  tube;  below  this  a  square  or  round 
stage,  with  a  central  opening;  under  the  stage,  a  condenser;  and  below  the 
condenser,  a  movable  mirror.  At  the  lower  end  of  the  tube  is  a  swinging  nose- 
piece,  into  which  the  lenses  are  to  be  screwed.  The  condenser  is  a  system  of 


GENERAL  DIRECTIONS  xj 

lenses  for  focusing  light  upon  the  stage.  Just  below  the  condenser  is  an  iris 
diaphragm;  holding  the  lens  in  the  top  of  the  tube  with  one  hand,  turn  the 
microscope  upside  down  so  that  you  can  see  the  diaphragm.  Note  that  the 
diaphragm  is  composed  of  movable  leaves  which  are  moved  by  a  button  at 
the  side  of  the  diaphragm.  Slide  the  button  back  and  forth  and  note  effect  on 
the  size  of  the  opening  formed  by  the  leaves.  The  mirror  has  two  surfaces, 
plane  and  concave.  When  the  condenser  is  in  use,  the  plane  surface  of  the  mirror 
is  to  be  employed,  as  the  concave  mirror  converges  the  light,  and  thus  conflicts 
with  the  action  of  the  condenser. 

2.  The  lenses.     Find  on  a  shelf  in  the  microscope  box,  two  cylindrical  metal 
cases.    Unscrew  these  and  remove  from  them  the  objectives.    These  objectives 
are  marked  3  and  7  (German  system)  or  16  mm.  and  4  mm.  (American  system). 
Note  that  3,  or  16  mm.,  is  shorter,  has  a  larger  lens,  and  is  therefore  of  a  lower 
power  of  magnification  than  7,  or  4  mm.     Screw  the  objectives  into  place  in  the 
nosepiece,  holding  each  with  both  hands  while  doing  so  to  avoid  possibility  of 
dropping. 

On  another  shelf  in  the  miscroscope  box  will  be  found  two  eyepieces  or  oculars. 
These  are  Nos  i  and  3,  or  4X  and  8X  ;  the  first-named  one  is  in  each  case  the 
lower  power.  Place  the  No.  i  or  4X  eyepiece  in  the  top  of  the  tube. 

3.  The  adjustment  screws.     On  the  arm  between  the  pillar  and  the  tube  is  a 
pair  of  vertical  screws.     These  move  the  tube  considerable  distances  at  each 
turn,  and  are  therefore  designated  as  the  coarse  adjustment.    At  the  top  of  the 
pillar  is  a  horizontal  screw,  the  fine  adjustment,  which  moves  the  tube  only  a 
very  short  distance  at  each  turn.     Turn  each  of  the  screws  and  note  the  effect 
on  the  tube.     When  the  fine  adjustment  is  turned  clockwise,  the  tube  moves 
down;  when  counter-clockwise,  it  moves  up. 

4.  To  use  the  low  power: 

a)  Swing  the  low-power  objective  into  place,  and  place  the  low-power  eye- 
piece in  the  top  of  the  tube. 

b)  While  looking  through  the  eyepiece,  turn  the  mirror  toward  the  light 
until  the  field  of  the  microscope  becomes  suddenly  bright. 

c)  Place  the  object  to  be  examined,  mounted  on  a  glass  slide,  in  the  center 
of  the  opening  on  the  stage. 

d)  While  watching  the  objective  from  the  outside,  lower  the  tube  by  means 
of  the  coarse  adjustment  until  the  objective  is  close  to  the  slide. 

e)  While  looking  into  the  eyepiece,  slowly  raise  the  tube  by  means  of  the 
coarse  adjustment  until  the  object  comes  into  view.     It  is  now  said  to  be  in  focus. 
Note  the  distance  from  the  object  at  which  the  lower  power  comes  to  focus. 

/)  Adjust  the  light  to  the  best  advantage  by  means  of  the  iris  diaphragm. 
This  is  a  very  important  point.  Students,  as  a  rule,  use  too  much  light,  which 
drowns  out  the  details  of  the  object  and  is  hard  upon  the  eyes.  Always  adjuM 
the  light  for  every  object  looked  at. 


rii  GENERAL  DIRECTIONS 

g)  If  the  object  is  very  transparent,  reduce  the  amount  of  light  before  begin- 
ning to  focus,  because  too  much  light  will  make  it  invisible.  Moving  the  slide 
slightly  while  trying  to  focus  will  facilitate  the  process. 

5.  To  use  the  high  power: 

a)  The  object  must  always  be  under  a  cover  glass  when  the  high  power  is  to 
be  used. 

b)  The  high  power  cannot  be  used  with  thick  or  thickly  mounted  objects. 

c)  The  object  to  be  viewed  must  always  be  found  first  with  the  low  power. 
Never  try  to  examine  anything  first  with  the  high  power.    Place  the  object  or  part 
of  the  object  which  you  desire  to  study  with  the  high  power  in  the  exact  center 
of  the  low-power  field. 

d)  Swing  the  nosepiece  around  so  that  the  high-power  objective  comes  into 
place. 

e)  The  object  should  now  be  nearly  in  focus  and  is  brought  into  exact  focus 
by  means  of  the  fine  adjustment.    If  the  object  is  not  in  focus  when  the  high 
power  is  swung  into  place,  the  microscope  is  not  perfectly  adjusted  and  the 
following  procedure  must  be  followed : 

(1)  The  center  of  the  field  of  the  high  power  may  not  be  the  same  as  the 
center  of  the  field  of  the  low  power.    The  object  will  therefore  not  be  in  the  field 
at  all  when  the  high  power  is  swung  around.    The  remedy  is  to  find  out  where  the 
center  of  the  high-power  field  is  on  the  low-power  field  and  to  place  the  object 
there  instead  of  in  the  center  when  preparing  to  use  the  high  power. 

(2)  The  focus  of  the  high  power  may  not  be  the  same  as  the  focus  of  the  low 
power.    This  is  the  common  difficulty.    The  remedy  is  to  screw  the  tube  up 
or  down  after  the  high  power  is  in  place  until  a  focus  is  obtained.    You  will 
have  to  find  out  by  trial  whether  to  screw  up  or  down.    If  up,  then  always 
remember  to  raise  the  tube  of  the  microscope  before  swinging  the  high  power 
into  place,  as  otherwise  the  objective  will  strike  against  the  slide. 

(3)  Have  the  assistant  help  you  find  out  the  peculiarities  of  your  microscope. 
/)  After  getting  a  focus,  adjust  the  amount  of  light  by  means  of  the  diaphragm. 

The  amount  of  light  best  for  the  high  power  is  never  that  best  for  the  low  power. 

g)  Note  how  close  to  the  slide  the  high-power  focuses.  For  this  reason  thick 
objects  cannot  be  viewed  under  the  high  power,  and  care  must  always  be  taken 
not  to  run  the  objective  into  the  slide,  as  this  will  break  the  slide  and  may  injure 
the  lens. 

6.  Plane  of  focus.  As  the  microscope  is  an  optical  instrument,  the  planes 
of  focus  of  its  lenses  are  geometrical  planes,  i.e.,  planes  without  thickness.  All 
objects  viewed  through  the  microscope  have  an  appreciable  thickness.  It  is 
therefore  obvious  that  no  object,  no  matter  how  thin  it  is,  can  be  seen  in  its  totality 
in  a  single  plane  of  focus,  as  some  parts  are  certain  to  lie  outside  that  plane. 
//  is  therefore  necessary  to  change  the  focus  continually  while  mewing  an  object  in 
the  microscope.  This  is  particularly  essential  when  using  high  powers.  Students 


GENERAL  DIRECTIONS  xiii 

almost  invariably  make  the  grave  mistake  of  getting  an  object  in  focus,  and  then 
examining  it  without  any  further  change  of  focus,  with  the  result  that  they  do  not 
see  all  parts  of  the  object,  nor  get  a  true  idea  of  the  relation  in  space  of  the  parts. 
The  practiced  microscopist  never  takes  his  hand  from  the  fine  adjustment  screw 
but  continually  changes  the  focus  as  he  looks.  The  student  should  at  once  form 
a  habit  of  doing  likewise. 

7.  Moving  the  slide.    As  the  image  in  the  microscope  is  reversed,  the  slide 
must  be  moved  in  the  opposite  direction  from  that  in  which  it  is  desired  to  move 
the  image.    This  will  soon  become  a  habit.     In  moving  a  slide,  do  not  put  both 
hands  upon  it  but  grasp  it  by  the  edges  between  the  thumb  and  index  ringer  of 
one  hand.    This  leaves  the  other  hand  free  to  shift  the  focusing  screw. 

8.  Miscellaneous  directions: 

a)  If  the  image  is  dim  or  indistinct,  or  if  the  field  rolls,  or  if  the  high  power 
cannot  be  focused,  then  in  all  probability  the  lens  is  dirty  or  wet.     Clean  it 
with  an  old,  soft  handkerchief.     If  after  cleaning  the  lens  the  high  power  will 
not  focus,  then  the  material  under  examination  is  too  thick  and  must  be  made 
thinner.     In  case  of  any  trouble  with  the  microscope,  don't  tamper  with  the 
instrument,  but  call  the  assistant. 

b)  If  images  of  buildings,  etc.,  appear  in  the  field,  they  may  be  obliterated 
by  using  the  concave  surface  of  the  mirror,  or  by  lowering  the  condenser. 

c)  In  working  with  artificial  light,  use  the  concave  surface  of  the  mirror. 

d)  Round  black  rings  in  the  field  are  air  bubbles  under  the  cover  glass. 

e)  If  the  fine  adjustment  turns  without  producing  any  effect  upon  the  tube, 
it  has  come  to  the  upper  limit  of  its  range  and  must  be  screwed  down.    If  it  will 
not  turn  at  all,  it  has  come  to  the  lower  limit  of  its  range  and  must  be  screwed  up. 

/)  Keep  the  microscope  clean  and  free  from  dust.  Do  not  let  it  stand  in  the 
sunlight.  Do  not  use  sunlight  for  illumination  in  looking  through  the  microscope. 

g)  Keep  both  eyes  open  when  looking  through  the  microscope.  If  you  find 
this  difficult,  try  placing  an  oblong  of  stiff  paper  around  the  top  of  the  microscope, 
so  that  the  unused  eye  will  not  see  objects. 

9.  The  magnification  of  the  low  power  is  about  50;  of  the  high  power,  500. 

KEEP  THE  LENSES  CLEAN 

ADJUST  THE  LIGHT  FOR  EVERY  OBJECT 

ADJUST  THE  FOCUS  CONTINUALLY  WHILE  YOU  LOOK 


•Ml 

I.  GENERAL  SURVEST  OF  THE  FROG  ..........  i 

A.  Killing  the  Frog x 

B.  External  Anatomy  of  the  Frog i 

C.  The  Buccal  or  Mouth  Cavity 4 

D.  Body  Wall,  Coelome,  Mesenteries 5 

E.  General  Internal  Structure 8 

II.  GENERAL  PHYSIOLOGY 14 

A.  Function  of  the  Nervous  System;  Irritability,  Conductivity      ....  14 

B.  Function  of  the  Muscular  System;  Contractility 15 

C.  Function  of  the  Digestive  System;  Digestion,  Absorption 16 

D.  Function  of  the  Respiratory  System;  Respiration,  Oxidation  18 

E.  Function  of  the  Excretory  System ;  Excretion 19 

F.  Function  of  the  Circulatory  System;  Circulation  of  the  Blood  ....  20 

G.  Function  of  the  Reproductive  System;    Reproduction,  Development,  the 
Life-Cycle 20 

H.  Summary  of  Physiological  Processes .23 

III.  GENERAL  HISTOLOGY:  CELLS  AND  TISSUES 24 

A.  Study  of  a  Typical  Cell 25 

B.  Studies  of  Tissues 26 

IV.  GENERAL  HISTOLOGY:  STRUCTURE  OF  ORGANS 33 

A.  Structure  of  the  Liver 33 

B.  Structure  of  the  Intestine 33 

C.  Structure  of  the  Stomach 35 

D.  Structure  of  the  Skin 3$ 

E.  Structure  of  the  Kidney 37 

F.  Structure  of  the  Spinal  Cord 38 

V.  THE  SPECIAL  ANATOMY  OF  THE  FROG 39 

A.  The  Digestive  System 39 

B.  The  Urinogenital  System 4° 

C.  The  Respiratory  System 4* 

D.  The  Circulatory  System:  the  Venous  System 4* 

E.  The  Circulatory  System:  the  Arterial  System 44 

F.  The  Circulatory  System:  the  Structure  of  the  Heart 45 

G.  The  Nervous  System .46 

H.  The  Skeleton 51 

I.  The  Muscular  System 55 

J.  General  Anatomical  Principles ^i 

VI.  THE  PROCESS  OF  CELL  DIVISION 

A.  Mitosis  in  the  Eggs  of  Ascaris 

B.  Mitosis  in  Plant  Root  Tips £4 

C.  Mitosis  in  the  Eggs  of  the  Whitefish 

XV 


xvi  TABLE  OF  CONTENTS 

PAGE 

VII.  GENERAL  EMBRYOLOGY    .............  65 

A.  Development  of  the  Starfish      .       ..........  65 

B.  Development  of  the  Frog  ............  66 

VIII.  HEREDITY:  MENDEL'S  LAW    ......      •      .....  69 

A.  First  Hybrid  Generation    ..........       .       .  69 

B.  Second  Hybrid  Generation        ...........  69 

IX.  PHYLUM  PROTOZOA    ....      ..........  71 

A.  Introductory  Remarks       ............  71 

B.  The  Amoeba        ..............  72 

C.  Paramecium  ...............  73 

D.  General  Study  of  Protozoan  Cultures      .........  78 

X.  PHYLUM  COELENTERATA  .............  82 

A.  Hydra    .    '   .               .............  82 

B.  A  Colonial  Coelenterate     ............  86 

C.  General  Survey  of  Other  Coelenterates    .........  88 

XI.  PHYLUM  PLATYHET.MTNTHES     ............  oo 

A.  Planaria        ...............  90 

B.  General  Survey  of  Other  Flat  worms        .........  93 

XII.  PHYLUM  ANNELIDA    ..............  95 

A.  Preliminary  Study  of  Nereis      ...........  95 

B.  The  Anatomy  of  the  Earthworm      ........  96 

C.  General  Survey  of  Annelids       ...........  105 


PHYLUM  ARTHROPODA       ..........      .      ..      .  106 

A.  The  Anatomy  of  the  Lobster  (or  Crayfish)     ........  106 

B.  The  Anatomy  of  the  Grasshopper     ..........  117 

C.  General  Survey  of  Arthropods  .....       ......  124 

XIV.  FINAL  EXERCISES  ON  COMPARATIVE  ANATOMY     ........  126 

A.  Comparison  of  Cross-Sections    ...........  126 

B.  Comparison  of  Functional  Systems  ..........  126 

XV.  EXERCISE  ON  CLASSIFICATION        ...........  127 

Key  to  the  Phyla  of  Animals  .......       .....  129 

Key  to  the  Classes  of  the  Principal  Phyla    .........  131 

XVI.  EXERCISE  ON  ECOLOGY     .       ............  135 

SUGGESTIONS  FOR  THE  LABORATORY  ASSISTANTS     .........  139 

INDEX     ...........  ...  145 


<S<  '  <-+>*• 

Gt^Cst- 1<. 

I.     GENERAL  SURVEY  OF  THE  FROG 

It  is  believed  that  the  best  introduction  to  the  science  of  zoology  is  the 
thorough  study  of  a  single,  relatively  complex  animal.  For  this  reason,  we  shall 
first  examine  in  detail  the  anatomy,  the  physiology,  and  the  microscopic  struc- 
ture of  one  of  the  commonest  animals,  the  frog.  After  learning  how  such  an 
animal  is  constructed  and  how  it  employs  the  structures  which  it  possesses,  we 
shall  be  in  a  position  to  understand  the  make-up  of  other  animals,  and  to  appre- 
ciate by  what  changes  and  alterations  these  have  been  built  up  from  an  extremely 
simple  starting-point. 

A.      KILLING  THE  FROG 

The  frog  may  be  killed  either  by  placing  it  for  15  to  20  minutes  in  a  closed 
vessel  with  a  wad  of  cotton  soaked  in  ether  or  chloroform,  or  by  the  method  of 
pithing.  In  pithing,  a  blunt  instrument  is  thrust  through  the  space  between 
the  posterior  end  of  the  skull  and  the  beginning  of  the  vertebral  column  and  the 
nervous  system  is  destroyed.  To  pith  a  frog,  grasp  the  animal  firmly  in  the 
left  hand  and  bend  the  head  down  by  placing  the  forefinger  across  the  snout. 
With  the  finger  or  a  blunt  instrument  feel  for  the  depression  between  the  posterior 
end  of  the  skull  and  the  first  vertebra  (it  is  located  at  about  the  level  of  the  fore 
limbs).  Cut  through  the  skin  at  this  place  with  a  scissors,  and  press  firmly 
upon  the  depression  with  a  blunt  instrument  until  the  instrument  breaks  through 
the  muscles  into  the  cavity  of  the  skull.  Then  thrust  the  instrument  forward 
into  the  brain  and  then  backward  into  the  spinal  cord,  moving  it  about  so  as  to 
mash  the  nervous  system  thoroughly.  The  best  instrument  for  pithing  is  a 
stout  wire  hairpin  or  a  blunted  hatpin.  If  the  pithing  is  properly  done,  spon- 
taneous movements  cease. 

After  either  pithing  or  etherization,  it  will  be  noted  that  many  of  the  activities 
of  the  frog  continue;  the  heart  keeps  on  beating  for  a  considerable  length  of 
time  and  movements  of  various  kinds  can  be  elicited  by  the  proper  procedure. 
Is  the  frog  dead?  What  is  meant  by  death  in  the  higher  animals?  Do  all 
parts  of  an  animal  die  at  the  same  time?  What  part  of  the  frog  is  really 
dead?  (A.) 

B.   EXTERNAL  ANATOMY  OF  THE  FROG 

Obtain  an  etherized  frog,  place  it  in  the  dissecting  pan,  and  carefully  note  the 
following  points.  Read  also  Holmes,  chapter  iii.  The  body  of  the  animal  con- 
sists of  a  flattened  head  and  a  short  somewhat  spindle-shaped  trunk.  There  is 


2  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

neither  neck  nor  tail.  Head  and  trunk  (also  neck  and  tail  when  present)  con- 
stitute the  axial  part  of  an  animal  while  the  limbs  are  designated  as  the  appendicu- 
lar  part.  The  head  is  the  anterior  end;  the  opposite  region  of  the  body  is  the 
posterior  end;  and  the  terms  "anterior"  and  "posterior"  are  also  employed  to 
indicate  the  relative  positions  of  other  structures  with  reference  to  head  or  tail, 
as,  for  instance,  one  would  say  that  the  fore  limbs  are  anterior  to  the  hind  limbs. 
The  back  or  upper  surface  is  the  dorsal  side;  the  lower  or  under  surface,  the 
ventral  side;  and  the  regions  between  these  are  referred  to  as  lateral.  The  middle 
of  the  dorsal  side  is  the  median  dorsal  line,  and  that  of  the  ventral  side,  the 
median  ventral  line.  A  plane  passing  through  these  two  lines  from  anterior  to 
posterior  end  is  the  median  sagittal  plane,  and  divides  the  animal  into  right  and 
left  halves.  If  these  two  halves  are  identical  or  nearly  so,  the  animal  is  said  to 
be  bilaterally  symmetrical.  Is  the  frog  bilaterally  symmetrical  as  far  as  you  can 
observe  from  its  external  anatomy?  Is  man?  There  are  several  other  types 
of  symmetry  among  animals,  one  of  which  will  be  met  with  later  in  the  course. 
An  imaginary  axis  in  the  sagittal  plane  is  the  antero-posterior  axis  or  sagittal 
axis.  Any  axis  in  the  median  plane  from  the  dorsal  to  the  ventral  side  is  a 
dorsoventral  axis;  from  the  median  plane  to  the  sides,  a  medio-lateral  axis,  etc. 

These  terms  are  applicable  to  the  vast  majority  of  animals,  and  the  structures 
of  animals  are  arranged  with  reference  to  such  planes  and  axes  oj  symmetry. 

Note  differences  in  color  between  the  dorsal  and  ventral  surfaces,  and  observe 
whether  the  color  pattern  is  the  same  on  all  individuals.  Read  Holmes  (p.  3 7) ,  on 
the  power  of  frogs  to  alter  their  color. 

The  head  ends  hi  a  triangular  snout  which  incloses  the  relatively  large  mouth 
cavity,  and  which  bears  on  its  anterior  extremity  two  small  openings,  the  nostrils 
or  external  nares.  These,  unlike  our  own,  can  be  opened  and  closed  by  lowering 
and  elevating  certain  bones  of  the  upper  jaw  (Holmes,  p.  171).  Posterior  to  the 
nares  are  the  large  prominent  eyes,  in  which  may  be  distinguished  the  golden 
iris,  surrounding  a  central  opening,  the  pupil.  The  eye  is  provided  with  the 
following  eyelids,  as  should  be  determined  by  lifting  each  with  a  forceps:  an 
upper  eyelid,  a  well-developed  fold  of  skin  which  covers  the  upper  portion  of  the 
eyeball;  a  lower  eyelid,  semicircular  in  shape,  representing  scarcely  more  than 
the  free  edge  of  the  skin;  and  the  nictitating  membrane,  a  thin,  transparent,  very 
extensible  membrane,  which  is  really  an  outgrowth  of  the  lower  lid.  A  vestige 
of  the  nictitating  membrane  is  present  in  our  own  eyes  as  a  small  crescent- 
shaped  fold  near  the  inner  corners. 

Obtain  a  living  frog,  gently  touch  an  eyeball  and  observe  the  action  of  the 
eyelids.  Which  eyelids  are  movable?  Stimulate  the  eyeball  more  strongly 
and  observe  that  the  whole  eye  can  be  dropped  down  into  the  mouth  cavity. 
The  socket  in  the  skull  which  holds  the  eye  is  designated  as  the  orbit. 

Returning  now  to  the  dead  specimen,  note  a  circular  area  of  tense  skin  just 
posterior  to  the  eye.  This  is  the  tympanic  membrane  or  drum  membrane  of  tin* 


GENERAL  SURVEY  OF  THE  FROG  3 

ear,  which  covers  the  cavity  of  the  middle  ear.  The  external  ear  and  the  passage 
leading  in  from  it,  prominent  in  ourselves,  are  entirely  wanting  in  the  frog.  Near 
the  center  of  the  drum  membrane,  a  small  projection  may  usually  be  noticed; 
this  is  the  end  of  the  columella,  a  small  bone  which  transmits  inwardly  the  vibra- 
tions of  the  tympanic  membrane. 

In  the  median  line  of  the  head,  slightly  anterior  to  the  level  of  the  eyes, 
a  small  light-colored  spot,  the  brow  spot,  may  usually  be  found.  In  dark  indi- 
viduals, however,  it  may  be  concealed  by  pigment.  In  the  embryonic  develop- 
ment of  the  frog,  this  spot  is  in  connection  with  a  portion  of  the  brain,  called 
the  pineal  body,  and  it  itself  is  the  useless  vestige  of  a  former  third  medially 
located  eye  (Holmes,  p.  64). 

On  the  dorsal  side  of  the  trunk  extending  posteriorly  from  the  eyes  note  two 
light-colored  ridges,  where  the  skin  is  much  thickened  owing  to  the  presence  of 
large  poison  glands  underneath.  These  ridges  are  called  the  dorsolateral  dermal 
plicae.  At  the  posterior  end  of  the  trunk  on  the  dorsal  side  between  the  bases 
of  the  hind  legs  is  a  small  opening,  the  anus,  which  is  the  end  of  the  digestive 
tract.  In  the  middle  of  the  back  a  characteristic  hump  is  present,  owing  to  an 
alteration  at  this  place  in  the  structure  of  the  vertebral  column  (see  a  dried 
skeleton,  or  consult  Holmes,  Fig.  63,  p.  230). 

The  fore  limb  is  short  and  consists  of  three  divisions,  upper  arm,  forearm, 
and  manus  or  hand.  How  many  fingers  has  the  hand  ?  To  which  of  your  fingers 
do  these  correspond  (Holmes,  p.  65)  ?  The  rudiment  of  the  missing  finger 
may  be  felt  under  the  skin  on  the  inner  side  of  the  hand  at  the  base  of  the  present 
first  finger,  and  may  be  seen  on  the  skeleton  of  the  hand  04).  In  the  male 
frog,  the  inner  finger  is  enlarged  and  swollen  at  the  base,  especially  during  the 
breeding  season. 

The  hind  limb  likewise  consists  of  three  parts,  thigh,  shank,  and  pes,  or  foot. 
The  ankle  is  remarkably  elongated.  There  are  five  toes  and  a  rudiment  of  sixth, 
called  the  prehallux,  may  be  felt  on  the  inner  side  of  the  smallest  toe,  which  cor- 
responds to  our  great  toe.  Such  additional  fingers  occur  not  infrequently  among 
the  vertebrates,  but  their  morphological  significance  is  unknown. 

The  skin  is  smooth,  slimy  in  life,  and  possesses  neither  hairs,  scales,  nor  claws. 
Note  that  in  general  it  is  more  loosely  attached  to  the  body  than  in  most  animals. 

Make  an  accurate  drawing  of  the  frog  from  the  dorsal  side,  putting  in  all  of 
the  structures  and  parts  which  have  been  mentioned.  Before  beginning  to 
draw  re-read  carefully  the  directions  about  drawings.  Label  this  and  all  sub- 
sequent drawings  fully. 

NOTE. — At  the  close  of  the  first  laboratory  period,  make  an  incision  about  one- 
half  inch  long  through  the  skin  only  of  the  left  abdominal  wall  of  your  frog  and 
place  the  animal  in  the  jar  of  preserving  fluid  which  will  be  assigned  to  you. 
The  animal  must  always  be  kept  in  this  jar  when  not  in  use.  It  must  never  be 
left  out  on  the  tables,  and  never  allowed  to  become  dry. 


4  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

C.      THE  BUCCAL  OR  MOUTH   CAVITY 

Note  that  the  two  jaws  fit  together  very  tightly;  this  is  essential  for  respira- 
tion, as  will  be  seen  later.  Open  the  mouth  to  its  widest  extent,  cutting  the 
angle  of  the  jaws  if  necessary  (A).  Consult  Holmes,  chapter  iv,  pp.  68-73. 

1.  Roof  of  the  mouth  cavity. — The  edge  of  the  upper  jaw  is  covered  by  a 
fold  of  skin,  the  upper  Up  fold.     Just  within  this  fold  and  concealed  by  it  is  a 
semicircular  row  of  teeth,  the  maxillary  teeth,  borne  upon  the  edges  of  the 
maxillary  and  premaxillary  bones  of  the  skull.     It  is  necessary  to  grasp  the  lip 
fold  with  a  forceps  and  pull  it  outward  in  order  to  reveal  the  teeth.     Obtain  a 
dried  skull,  examine  the  teeth  with  a  hand  lens,  and  note  the  following  points. 
The  teeth  are  not  set  into  sockets,  that  is,  cavities  in  the  jaw,  as  are  our  own  teeth, 
but  they  are  fused  by  their  bases  and  sides  to  the  margins  of  the  jaw,  only  their 
tips  projecting  freely  above  the  edge  of  the  bone.     Each  tooth  is  a  hollow  cone, 
consisting  of  two  parts  separated  by  an  indistinct  groove:   an  upper  part,  the 
crown,  composed  of  dentine,  and  coated  externally  with  a  shiny  material,  the 
enamel;  and  a  lower  part,  the  root,  composed  of  cement.     The  teeth  are  replaced 
when  lost  and  two  or  three  sets  of  new  teeth  may  usually  be  seen  at  the  bases  of 
the  old  ones. 

Returning  now  to  your  own  specimen,  locate  within  the  row  of  maxillary 
teeth  a  deep  groove,  the  sulcus  marginalis.  At  the  tip  of  the  jaw  this  groove 
deepens  into  a  pit,  the  median  subrostral  fossa;  on  each  side  of  this  is  an  eleva- 
tion, the  subrostral  puhinar  or  cushion;  and  lateral  and  adjacent  to  this  is  another 
depression,  the  lateral  subrostral  fossa. 

Within  the  sulcus  marginalis  is  the  roof  of  the  mouth  cavity,  properly  speak- 
ing. The  anterior  extremity  of  this  is  occupied  by  two  oval  openings,  the  internal 
nares  or  choanae;  they  are  the  internal  openings  of  the  cavities  of  the  nose,  whose 
external  openings  were  already  noted.  The  two  pairs  of  nares,  therefore,  with 
the  cavities  of  the  nasal  chambers,  constitute  the  respiratory  passage  through 
which  air  is  drawn  into  the  buccal  cavity.  Between  the  choanae  are  two  patches 
of  wmerine  teeth,  located  upon  the  wmer  bone.  The  greater  part  of  the  roof  of 
the  mouth  is  occupied  by  two  large  rounded  prominences,  where  the  eyes  are 
located,  and,  as  already  observed,  the  eyes  can  be  withdrawn  into  the  mouth 
cavity.  At  each  side  of  the  posterior  end  of  the  roof  is  an  opening,  the  entrance 
to  the  Eustachian  tube  (auditory  tube  in  more  recent  terminology).  Where  does 
it  lead  ?  Consult  Holmes,  p.  69. 

2.  Floor  of  the  mouth  cavity. — The  edge  of  the  lower  jaw  forms  a  ridge 
which  fits  into  the  sulcus  marginalis.     At  the  tip  of  the  lower  jaw  is  an  elevation, 
the  prelingual  tubercle,  and  on  each  side  of  this  a  depression,  the  prelingual  fossa. 
Note  how  exactly  these  fit  into  the  elevations  and  depressions  of  the  upper  jaw. 
Are  teeth  present  on  the  lower  jaw  ?    The  greater  part  of  the  floor  of  the  mouth 
is  occupied  by  the  tongue.    Note  the  size,  shape,  and  attachment  of  this  organ, 
and  find  out  how  it  is  used  in  catching  prey  (Holmes,  pp.  26,  70-71).     Turn  the 


GENERAL  SURVEY  OF  THE  FROG  5 

tongue  forward  and  feel  the  floor  of  the  mouth  behind  the  tongue.  It  is  stiffened 
by  a  cartilaginous  plate,  the  body  of  the  hyoid,  whose  anterior  end  is  hollowed 
out  to  receive  the  base  of  the  tongue,  and  gives  off  a  pair  of  slender  curving 
processes,  the  anterior  horns  of  the  hyoid,  which  extend  posteriorly  to  the  ears. 
Scrape  away  the  membrane  from  the  floor  of  the  mouth  in  order  to  see  these 
structures  more  clearly.  Posterior  to  the  body  of  the  hyoid  in  the  median  line 
is  a  circular  hardened  elevation,  the  laryngeal  prominence,  which  bears  in  its 
center  an  elongated  slit,  the  glottis.  Where  does  the  glottis  lead  ?  At  the  back 
of  the  mouth  cavity,  roof  and  floor  converge  to  a  large  opening,  the  beginning  of 
the  esophagus,  the  first  portion  of  the  digestive  tract.  In  the  male  frog,  the 
slitlike  opening  of  the  vocal  sac  is  present  on  each  side  of  the  floor  near  the  edge 
of  the  jaw,  on  a  level  with  the  glottis.  On  the  use  of  the  vocal  sacs  in  croaking, 
see  Holmes  (p.  167). 

Draw  the  floor  and  roof  of  the  mouth. 

D.      BODY  WALL,    COELOME,   MESENTERIES 

i.  Structure  of  the  body  wall  (see  Holmes,  chap,  iv,  pp.  73-80). — Remove 
the  skin  slowly  from  the  trunk  of  the  frog,  noting  carefully  at  what  places  the 
skin  is  attached  to  the  underlying  parts  by  means  of  weblike  partitions.  (While 
doing  this  note  also  the  blood  vessels  to  the  skin  described  in  the  next  paragraph, 
and  in  the  median  dorsal  line,  the  sensory  nerves  passing  in  pairs  from  the  skin 
into  the  vertebral  column.)  The  space  under  the  skin  is  divided  by  these  parti- 
tions into  compartments,  called  the  subcutaneous  lymph  spaces,  or  lymph  sacs, 
which  in  life  are  filled  with  a  fluid,  the  lymph.  Compare  your  observations  with 
Holmes  (Fig.  78,  p.  281),  and  read  what  Holmes  says  about  the  lymphatic 
system.  The  lymph  is  similar  in  composition  to  and  derived  from  the  blood, 
except  that  it  contains  no  red  blood  corpuscles.  It  is  in  direct  contact  with  the 
living  substance  to  which  it  supplies  food  and  oxygen,  and  from  which  it  removes 
waste  products.  The  frog  and  its  relatives  differ  from  other  vertebrates  in  this 
enormous  development  of  huge  lymph  spaces,  not  only  under  the  skin,  but  also 
throughout  the  body.  This  structural  feature  is  probably  associated  with  the 
amphibious  habits  of  these  animals. 

In  removing  the  skin,  note  the  extensive  supply  of  blood  vessels  to  the  skin, 
and  particularly  the  following  two  large  vessels:  the  musculo-cutaneous  vein, 
which  runs  posteriorly  in  the  muscles  of  the  ventro-lateral  region  of  the  body 
wall,  and  then  turns  and  passes  to  the  skin  in  the  partition  between  the  abdominal 
and  lateral  lymph  sacs;  and  the  cutaneous  artery,  which  emerges  in  front  of  the 
shoulder  and  supplies  the  skin  of  the  dorsal  side.  This  relatively  large  develop- 
ment of  skin  blood  vessels  is  due  to  the  respiratory  function  of  the  skin,  to  be 
discussed  more  fully  later. 

The  removal  of  the  skin  exposes  the  muscles  of  the  body  wall  and  the  skeleton 
which  they  inclose  and  to  which  they  are  attached.  The  principal  parts  of  the 


6  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

skeleton  may  be  felt  imbedded  if.  the  muscles.  Identify  them  as  follows  with 
the  aid  of  Holmes  (Fig.  63,  p.  230).  The  head  contains  a  bony  case,  the  skull, 
to  which  the  upper  jaw  is  immovably  fused,  while  the  lower  jaw  is  hinged  to  it 
by  a  joint.  A  bony  arch,  the  pectoral  girdle,  supports  the  fore  limbs.  Feel  this 
on  both  dorsal  and  ventral  sides  at  the  level  of  the  fore  limbs.  On  the  dorsal 
side,  the  girdle  terminates  in  a  flat  thin  bone  with  a  cartilaginous  border,  called 
the  suprascapula.  Ventrally,  the  bones  of  the  girdle,  covered  by  the  pectoral 
muscles,  are  seen  to  be  articulated  to  a  slender  chain  of  bones  and  cartilages 
which  occupies  the  median  ventral  line  and  ends  anteriorly  and  posteriorly  with 
conspicuous  rounded  cartilaginous  expansions.  This  whole  structure  is  called 
collectively  the  sternum,  or  breastbone  (see  Holmes,  Fig.  67,  p.  239).  The  hind 
limbs  are  similarly  supported  by  the  pelvic  girdle.  Feel  for  this  on  both  sides; 
ventrally  it  forms  a  hard  crest  between  the  bases  of  the  hind  legs;  dorsally 
two  of  its  bones,  the  ilium  bones,  extend  forward,  producing  the  two  conspicuous 
lateral  ridges  on  the  lower  half  of  the  back.  The  median  dorsal  line  is  depressed, 
forming  a  groove.  Pass  the  point  of  an  instrument  along  this  groove  and  feel 
the  vertebral  column  lying  underneath,  and  its  lateral  expansions,  the  transverse 
processes.  The  last  pair  of  these  has  enlarged  bulbous  ends,  which  are  really 
rudimentary  ribs,  to  which  the  anterior  ends  of  the  ilium  bones,  mentioned  above, 
are  firmly  attached.  It  is  this  region  which  produces  the  external  hump  in  the 
frog.  Posterior  to  this  point,  the  median  line  is  occupied  by  a  long  slender  bone, 
which  has  been  produced  by  the  fusion  of  a  number  of  vertebrae;  it  is  called 
the  urostyle. 

The  lateral  and  ventral  abdominal  walls  are  supported  by  muscles  only, 
skeleton  being  absent.  There  are  several  layers  of  these  muscles,  the  external 
layer  consisting  of,  laterally,  the  external  oblique  muscle;  ventrally  on  each  side 
of  the  median  line,  the  segmented  rectus  abdominis  muscle  extending  from  the 
pelvic  girdle  to  the  sternum;  and  between  these,  and  partially  covering  the 
external  oblique,  a  posterior  slip  from  the  pectoral  muscles.  A  flat,  thin  muscle, 
the  mylohyoid,  extends  transversely  across  the  ventral  side  .of  the  lower  jaw. 
This  arrangement  of  the  ventral  musculature  is  very  similar  to  that  of  all  verte- 
brates, including  man.  The  median  ventral  line  from  the  pelvic  girdle  to  the 
posterior  expansion  of  the  sternum  is  occupied  by  a  white  strip,  the  linea  alba, 
under  which  there  runs,  in  the  frog,  a  conspicuous  blood  vessel,  the  anterior 
abdominal  vein.  For  further  details  and  a  picture  of  the  foregoing  features, 
see  Holmes  (Fig.  70,  p.  249). 

Cut  through  the  muscles  on  the  ventral  side  to  the  left  (frog's  left)  of  the  linea 
alba  from  a  point  just  in  front  of  the  pelvic  girdle  up  to  the  mylohyoid  muscle, 
cutting  through  the  pectoral  girdle.  A  large  cavity,  the  body  cavity,  coelome,  or 
pleuroperitoneal  cavity,  which  contains  the  internal  organs,  or  viscera,  is  thus 
exposed.  This  space  is  lined  by  a  smooth  shining  membrane,  the  pleuroperi- 


GENERAL  SURVEY  OF  THE  FROG  7 

toneum  (frequently  but  less  correctly  called  for  brevity  peritoneum).  It  should 
be  recalled  that  in  man  the  body  cavity  is  divided  by  means  of  a  muscular  parti- 
tion, the  diaphragm,  into  two  completely  separated  portions,  an  anterior  thoracic 
cavity  and  a  posterior  abdominal  cavity.  The  lining  membrane  of  the  former  is 
then  called  pleura,  and  that  of  the  latter,  peritoneum,  in  the  correct  sense.  Since, 
however,  in  the  lower  vertebrates,  including  the  frog,  a  diaphragm  has  not  yet 
evolved,  one  continuous  coelome,  or  pleuroperitoneal  cavity,  is  present,  and  its 
lining  membrane  is  named  the  pleuroperitoneum. 

The  body  wall  thus  consists  of  three  layers:  the  skin,  the  muscles  with  their 
contained  skeleton,  and  the  coelomic  lining,  or  peritoneum,  with  the  subcutaneous 
lymph  spaces  lying  between  the  first  two  layers. 

2.  The  peritoneum  and  mesenteries. — The  peritoneum  not  only  lines  the 
coelome,  but  forms  a  close  investment  of  all  the  viscera,  for  which  purpose  it  is 
frequently  pulled  away  from  the  body  wall  as  a  double-walled  membrane.  That 
portion  of  the  peritoneum  which  adheres  to  the  inside  of  the  body  wall  is  called 
the  parietal  peritoneum;  that  which  invests  the  viscera  is  the  visceral  peritoneum, 
or  serosa;  and  that  which  extends  from  the  body  wall  to  the  individual  organs 
or  from  one  organ  to  another  is  a  mesentery  or  ligament.  In  the  formation  of  a 
mesentery,  the  peritoneum  leaves  the  body  wall,  passes  over  the  surface  of  the 
organ,  and  returns  to  the  body  wall  at  the  same  point  from  which  it  left,  produ- 
cing a  double-walled  membrane  between  the  organ  and  the  body  wall.  It  is  thus 
evident  that  the  peritoneum  is  everywhere  continuous  and  unbroken,  and  that 
the  viscera  are  really  outside  of  the  peritoneum,  which  forms  a  closed  sac  into 
which  the  viscera  appear  to  be  pushed  from  without.  The  condition  is  not  really 
brought  about  in  this  way  but  by  the  fact  that  the  peritoneum  develops  later 
than  the  viscera  and  closes  over  them  after  they  have  formed.  The  visceral 
peritoneum  is  so  tightly  applied  to  the  surface  of  the  viscera  that  it  cannot  be 
separated  from  them. 

Extreme  caution  must  be  used  in  examining  the  following  mesenteries, 
especially  those  in  the  region  of  the  heart,  so  as  not  to  destroy  them. 

Note  the  following  mesenteries.  Lift  up  the  pectoral  girdle  cautiously  and 
find  beneath  it  a  thin-walled  sac,  the  pericardial  sac,  which  contains  the  heart. 
Pick  up  the  pericardial  sac  gently  with  a  forceps  and  observe  that  it  is  separated 
from  the  heart  by  a  space,  the  pericardial  cavity,  in  which  the  heart  moves  freely. 
The  heart  is  in  reality,  like  the  other  viscera,  inclosed  in  a  double  sac;  the  inner 
one  tightly  invests  the  heart,  constituting  in  fact  a  serosa,  or  visceral  pericardium; 
the  outer  sac  as  already  noted  is  loose  and  separated  from  the  heart  by  the  peri- 
cardial cavity,  forming  a  parietal  pericardium.  The  pericardium  is  therefore  a 
part  of  the  genera  lining  of  the  coelome,  and  the  pericardial  cavity  is  a  part  of 
the  coelomic  cavity,  from  which,  however,  it  has  become  completely  separated 
during  embryonic  development,  by  the  formation  of  the  pericardial  sac  (parietal 
pericardium). 


8  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

The  general  pleuroperitoneal  membrane  in  the  region  of  the  heart  leaves  the 
body  wall  in  the  median  dorsal  line  and  passes  ventrally  on  each  side  of  the  peri- 
cardial  sac  and  in  inseparable  contact  with  it;  the  two  sides  then  meet  ventrally 
below  the  heart  and  form  a  double  membrane  which  extends  vertically  from  the 
pericardial  sac  to  the  ventral  median  line  under  the  sternum.  This  vertical 
membrane  also  supports  the  liver,  the  large  reddish-brown  organ  around  and 
posterior  to  the  heart,  and  this  part  of  it  is  therefore  known  as  the  suspensory 
or  falciform  ligament  of  the  liver.  Follow  the  suspensory  ligament  posteriorly 
along  the  median  ventral  line  and  note  that  it  supports  the  large  anterior 
abdominal  vein  which  was  mentioned  in  the  preceding  section.  Follow  along 
the  median  ventral  line  and  at  the  posterior  end  of  the  coelome  locate  the  median 
ligament  of  the  bladder,  a  mesentery  which  attaches  the  urinary  bladder,  a  thin- 
walled,  often  shriveled  sac,  to  the  ventral  body  wall. 

There  was  originally  in  the  embryo,  a  complete  double-walled  mesentery 
running  from  the  median  dorsal  line  to  the  median  ventral  line,  and  inclosing  the 
viscera  between  its  two  walls.  The  coelome  was  thus  divided  into  two  entirely 
separated  halves.  The  portion  of  this  mesentery  between  the  digestive  tract 
and  the  dorsal  wall  is  called  the  dorsal  mesentery,  and  that  from  the  digestive 
tract  to  the  ventral  wall,  the  ventral  mesentery.  The  dorsal  mesentery,  as  will 
be  seen  shortly,  is  still  intact  in  the  adult  frog,  but  the  ventral  mesentery  has 
entirely  disappeared,  except  for  certain  remnants  already  mentioned — the 
suspensory  ligament  of  the  liver,  and  the  ligaments  of  the  bladder,  and  certain 
ligaments  running  from  the  liver  to  the  intestine,  which  will  be  described  below. 

Cut  through  the  ventral  mesenteries,  and  pin  out  the  body  wall,  making 
crosscuts  if  necessary  so  that  the  viscera  will  be  fully  exposed. 

E.      GENERAL  INTERNAL  STRUCTURE 

The  frog  is  made  up  of  a  number  of  definite  structures  called  organs,  each  of 
which  has  a  definite  function  to  perform.  Ah1  of  the  organs  which  aid  in  per- 
forming the  same  function  are  grouped  together  as  a  system  or  tract.  The  organs 
constituting  one  system  may  be  all  alike  or  may  be  different  among  themselves. 
In  general  in  a  complex  animal  there  are  ten  systems:  skin  and  its  derivatives, 
skeletal,  muscular,  digestive,  circulatory,  respiratory,  excretory,  reproductive,  nervous, 
and  sensory  systems.  To  this  list,  there  should  probably  be  added,  in  the  case 
of  vertebrates,  an  eleventh,  composed  of  a  number  of  glands,  which  were  originally 
derived  from  the  other  systems,  but  have  lost  connection  with  them  and  have 
taken  on  peculiar  but  extremely  important  functions.  This  group  of  glands  is 
spoken  of  collectively  as  the  glands  of  internal  secretion,  also  as  cryptoretic  or 
endocrinous  organs.  Attention  has  already  been  called  to  the  muscular  and 
skeletal  systems;  the  other  systems  will  now  be  described  briefly  and  will  be 
studied  in  detail  later  (Holmes,  chap,  iv,  pp.  73-80). 


GENERAL  SURVEY  OF  THE  FROG  g 

1.  Circulatory  system.— This  consists  of  the  heart,  the  arteries  (vessels  leaving 
the  heart),  the  veins  (vessels  entering  the  heart),  and  the  capillaries  (microscopic 
vessels  between  the  ends  of  the  arteries  and  the  beginnings  of  the  veins) .    Remove 
the  pericardium  by  cutting  it  off  with  a  fine  scissors,  and  examine  the  heart. 
The  chambers  of  the  heart  are  called  ventricle,  auricles,  sinus  venosus,  and  conus 
arteriosus.     The  ventricle  is  the  posterior,  thick-walled,  conical  portion,  the 
point  of  the  cone  being  designated  as  the  apex  of  the  ventricle,  and  the  base  of 
the  cone,  the  base.     The  auricles  are  the  two  dark-colored,  thin-walled  sacs 
anterior  to  the  ventricle.     Extending  from  the  right  side  of  the  base  of  the 
ventricle  obliquely  forward  between  the  auricles  is  a  tube,  the  conus  arteriosus, 
which  forks  into  two  trunks  leading  away  from  the  heart  (Holmes  and  most  other 
textbooks  erroneously  refer  to  this  chamber  of  the  heart  as  the  bulbus  arteriosus). 
To  locate  the  sinus  venosus,  turn  the  heart  up  so  that  the  apex  points  anteriorly, 
and,  putting  the  heart  on  a  stretch,  identify  a  small  chamber  appearing  as  a 
dorsal  and  posterior  continuation  of  the  auricles,  from  which,  however,  it  is 
separated  by  a  distinct  white  line.     Three  veins,  dark  red  tubes,  will  be  seen 
emerging  from  the  liver  to  enter  the  sinus  venosus  at  its  posterior  border,  and 
each  of  its  sides  receives  a  vein  which  runs  along  the  margin  of  the  adjacent 
auricle.     Through  these  large  veins  all  of  the  venous  blood  in  the  body  is  returned 
to  the  sinus  venosus  which  passes  it  on  into  the  right  auricle.     Note  the  mem- 
brane by  which  the  pericardial  sac  is  attached  to  the  serosa  of  the  liver;  this  is 
the  coronary  ligament  of  the  liver. 

2.  Respiratory  system. — This  system  consists  of  the  glottis,  noted  in  the 
study  of  the  floor  of  the  mouth,  a  pair  of  lungs,  and  the  larynx,  a  chamber  con- 
necting the  lungs  with  the  glottis.     The  lungs  will  be  found  attached  to  the 
anterior  wall  of  the  coelome,  lateral  to  the  heart.     Push  the  liver  and  other 
structures  aside  in  order  to  see  them.     Each  is  closely  invested  by  a  sac  of 
peritoneum.     The  larynx  will  be  studied  later. 

3.  Digestive  system. — Its  parts  are  the  esophagus,  stomach,  small  intestine, 
large  intestine,  and  digestive  glands.    The  esophagus  lies  dorsal  to  the  heart  and 
will  be  seen  more  clearly  at  a  later  time.     It  passes  into  the  elongated  cylindrical 
stomach,  a  conspicuous  white  organ  on  the  left  side  of  the  body  dorsal  to  the 
liver.     (If  the  animal  is  a  female,  the  large  ovaries,  voluminous  lobed  black  and 
white  masses,  will  obscure  the  rest  of  the  abdominal  viscera,  and  may  be  removed, 
at  least  on  the  left  side.)     From  the  end  of  the  stomach,  trace  the  small  intestine, 
a  coiled  tube,  to  its  enlargement  into  the  large  intestine.    Locate  the  urinary 
bladder,  a  thin-walled,  usually  shriveled  sac  at  the  extreme  posterior  end  of  the 
coelome.     The  large  intestine  passes  through  the  bony  ring  formed  by  the  pelvic 
girdle,  and  opens  to  the  exterior  through  the  anus.     The  entire  tube  from  mouth 
to  anus  is  the  alimentary  canal.     Associated  with  the  alimentary  canal  are  two 
digestive  glands,  the  liver,  already  noted,  and  the  pancreas.    The  latter  is  a 


io  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

yellowish,  very  irregular  body,  lying  in  the  mesentery  which  extends  between 
the  liver,  the  small  intestine,  and  the  stomach.  The  first  part  of  the  small 
intestine,  called  the  duodenum,  will  be  found  to  bend  abruptly  forward 
toward  the  liver,  and  in  the  mesentery  between  this  bent  portion  of  the 
small  intestine  and  the  stomach  is  located  some  yellowish  branching  material 
which  constitutes  the  pancreas.  Between  the  lobes  of  the  liver  lies  the  round 
green  gall  bladder. 

The  following  mesenteries  should  be  carefully  identified,  and  each  organ 
picked  up  with  a  forceps  as  you  read  the  description,  and  its  relation  to  the  body 
wall  and  other  organs  noted.  The  entire  alimentary  canal  is  suspended  from  the 
median 'dorsal  line  of  the  coelome  by  an  extensive  mesentery,  the  dorsal  mesentery, 
in  which  run  the  blood  vessels,  lymphatics,  nerves,  etc.,  that  supply  the  digestive 
system.  Pick  up  the  stomach  and  intestine  with  a  forceps  and  see  how  they  are 
attached  to  the  dorsal  median  line  by  this  mesentery,  a  very  delicate  and  trans- 
parent membrane.  The  part  of  the  mesentery  which  supports  the  esophagus 
is  called  the  meso-esophageum;  the  stomach,  mesogastrium,  or  mesogaster;  the 
small  intestine,  mesenterium,  or  mesentery  proper;  and  the  large  intestine, 
mesorectum.  The  small  red  body  located  in  the  mesorectum  is  the  spleen,  an 
organ  associated  with  the  lymphatic  system.  Pick  up  the  urinary  bladder -with 
a  forceps,  and  find  its  attachments  to  the  ventral  median  line  by  the  median 
ligament  of  the  bladder,  already  noted;  to  the  large  intestine  by  the  rectovesical 
ligament;  and  to  the  lateral  body  wall  on  each  side  by  the  lateral  ligaments  of  the 
bladder.  The  liver  is  connected  to  the  dorsal  wall  of  the  coelome  by  the  dorsal 
mesentery  of  the  liver  or  mesohepar;  to  the  pericardial  sac  by  the  coronary  liga- 
ment; to  the  digestive  tract  mainly  by  the  hepato-gastro-duodenal  ligament  in 
which  the  pancreas  is  located;  and  to  the  ventral  wall  in  the  median  line  by  the 
suspensory  ligament,  previously  noticed  and  cut.  The  student  will  perceive 
that  the  ligaments  of  the  bladder,  and  the  suspensory  and  hepato-gastro-duodenal 
ligaments  are  remnants  of  an  originally  more  extensive  ventral  mesentery,  which 
connected  the  alimentary  canal  and  all  structures  ventral  to  it  to  the  ventral 
body  wall. 

The  mesenteries  constitute  an  ingenious  device  which  permits  the  viscera 
to  adjust  themselves  to  movements  of  the  body  and  to  carry  out  their  own  move- 
ments freely,  and  yet  at  the  same  time  holds  them  in  place  with  reference  to  each 
other  and  to  the  body  wall. 

4.  Reproductive  system. — This  system  consists  of  a  pair  of  reproductive 
glands,  or  gonads,  in  which  the  sexual  elements  are  produced,  and  a  pair  of  ducts 
which  convey  these  elements  to  the  exterior. 

The  female  gonads,  or  ovaries,  are,  in  the  mature  female,  the  most  conspicuous 
organs  in  the  body.  Each  is  a  large,  lobed  mass  composed  mainly  of  numerous 
black  and  white  eggs,  or  ova.  Each  is  suspended  from  the  dorsal  wall  by  a 


GENERAL  SURVEY  OF  THE  FROG  n 

mesentery,  the  mesovarium.  Lateral  to  each  ovary  is  its  duct,  the  oviduct,  a 
conspicuous  white,  much-coiled  tube,  also  supported  by  a  mesentery,  the  meso- 
tubarium. 

The  male  gonads,  or  testes,  are  a  pair  of  small,  oval  yellow  bodies  situated 
close  to  the  dorsal  body  wall  near  the  median  line.  The  intestine  must  be  pushed 
away  to  see  them.  Each  has  a  short  mesentery,  the  mesorchium.  The  testes 
have  no  ducts  but  the  male  reproductive  elements  pass  to  the  exterior 
through  the  ducts  of  the  kidneys,  which  will  be  identified  in  the  next  section. 
In  our  common  species  of  frog,  Rana  pipiens,  the  male  possesses  a  vestigial 
oviduct,  a  distinct  though  small  white  tube  running  along  the  lateral  border 
of  each  testis. 

Attached  to  the  anterior  end  of  each  testis,  and  in  a  similar  position  in  the 
female  frog,  is  a  fat  body,  consisting  of  a  tuft  of  yellow,  finger-shaped  processes. 
This  organ  is  a  storehouse  for  nutritive  material,  and  its  size  varies  with  the 
physiological  condition  of  the  frog,  being  very  small  in  the  spring  and  very  large 
in  the  fall  before  hibernation  begins. 

5.  Excretory  system. — It  is  composed  of  a  pair  of  kidneys  and  their  ducts. 
Turn  all  of  the  abdominal  viscera  to  the  right,  and  follow  the  peritoneum  along 
the  left  lateral  wall  of  the  coelome  around  to  the  dorsal  side.     Note  that  the 
peritoneum  leaves  the  body  wall  dorsally  and  stretches  as  a  thin  membrane 
across  the  dorsal  side  of  the  body  cavity,  leaving  a  large  space  between  itself 
and  the  muscles  of  the  dorsal  wall.     This  space  is  called  the  subvertebral  lymph 
sinus,  or  cisterna  magna,  and,  like  the  subcutaneous  lymph  spaces,  it  is  a  part 
of  the  extensive  lymphatic  system  which  the  frog  possesses.     Within  the  cisterna 
magna,  certain  structures,  including  the  kidneys,  are  located.     Such  structures 
are  said  to  be  retro  peritoneal,  i.e.,  they  lie  behind  the  peritoneum.      Break 
through  the  peritoneum  which  forms  the  ventral  wall  of  the  cisterna  magna,  and 
locate  in  the  cavity  of  the  cisterna  magna  the  kidneys,  a  pair  of  elongated,  flat, 
red  bodies  situated  close  to  the  peritoneum,  which  passes  across  their  ventral 
faces.     From  the  lateral  posterior  edge  of  each  kidney  arises  its  duct,  the  ureter, 
or  Wolffian  duct,  which  empties  into  the  large  intestine.     The  ureters  not  only 
carry  the  urine  from  the  kidneys  to  the  exterior,  but  also  transport  the  male 
reproductive  elements.     Owing  to  this  close  connection  which  exists  between  the 
excretory  and  reproductive  systems  in  all  vertebrates,  the  two  systems  are  com- 
monly referred  to  as  the  urinogenital  system.     The  urinary  bladder,  although 
functionally  a  part  of  the  excretory  system,  is  morphologically  a  saclike  out- 
growth of  the  ventral  wall  of  the  large  intestine. 

6.  Glands  of  internal  secretion.— Under  this  head  are  gathered  together  a 
number  of  glandlike  bodies  which  secrete  into  the  blood  certain  substances  of 
very  great  physiological  importance.     The  adrenal  gland  forms  a  bright  yellow 
stripe  on  the  ventral  face  of  each  kidney.     The  spleen,  which  may  be  a  gland  of 


12  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

internal  secretion  as  well  as  a  lymphatic  organ,  has  already  been  noted.  The 
pseudothyroids  are  a  pair  of  small  round  reddish  masses,  one  on  each  side  a  little 
anterior  to  the  heart,  at  about  the  level  of  the  posterior  end  of  the  body  of  the 
hyoid.  A  thyroid  gland  is  located  directly  under  each  pseudothyroid,  much 
deeper  down  in  contact  with  the  hyoid  cartilage  (see  Holmes,  Fig.  60,  p.  222). 
It  is  generally  difficult  to  identify  the  thyroid  glands  with  certainty.  For  the 
location  of  other  ductless  glands  of  the  frog  and  for  a  discussion  of  their  functions 
consult  Holmes,  chapter  xii,  p.  219. 

7.  Nervous  system. — The  nervous  system  is  divisible  into  three  parts:   the 
central  nervous  system,  consisting  of  the  brain  and  the  spinal  cord;  the  peripheral 
nervous  system,  consisting  of  the  nerves  which  pass  from  the  brain  (cranial 
nerves)  and  from  the  spinal  cord  (spinal  nerves)  to  all  parts  of  the  body;   and 
the  sympathetic  system,  an  outgrowth  of  the  central  nervous  system,  differentiated 
to  control  the  involuntary  activities  of  the  body  (as  digestive  tract,  heart,  etc.). 

Turn  the  frog  back  upward  and  remove  the  muscles  from  the  head  and 
median  portion  of  the  back.  This  exposes  the  skull  in  the  head,  and  a  row  of 
spinelike  projections  in  the  median  line  of  the  back,  which  are  the  neural  arches 
of  the  vertebrae.  Between  the  posterior  end  of  the  skull  and  the  first  vertebra 
is  a  space.  Insert  one  blade  of  a  fine  scissors  in  this  space,  keeping  the  point 
well  up  against  the  bone  to  avoid  punching  it  into  the  soft  brain  underneath,  and 
cut  away  the  roof  of  the  skull.  The  white-lobed  brain  lying  in  a  cavity  in  the 
skull  is  thus  revealed.  Its  parts  will  be  studied  later.  Similarly,  cut  posteriorly 
through  the  arches  of  the  vertebrae,  first  on  one  side,  then  on  the  other,  removing 
their  median  portions,  piece  by  piece.  The  neural  arches  of  the  vertebrae  are 
thus  seen  to  inclose  a  continuous  space,  the  neural  canal,  in  which  the  spinal  cord 
is  situated. 

The  cranial  nerves  cannot  be  observed  at  present.  The  spinal  nerves  arise 
in  pairs  from  the  spinal  cord  at  regular  intervals,  one  pair  emerging  between 
two  successive  vertebrae.  Turn  the  frog  ventral  side  up  and  look  into  the 
cisterna  magna.  The  stout  white  cords  which  appear  here  closely  applied  to  the 
muscles  of  the  dorsal  body  wall  are  the  most  posterior  spinal  nerves. 

The  sympathetic  nervous  system  consists  mainly  of  a  nervous  strand  on 
either  side  of  and  ventral  to  the  spinal  column.  At  regular  intervals  along  these 
strands  there  occur  enlargements,  or  ganglia,  each  of  which  connects  by  means 
of  a  nerve,  the  ramus  communicans,  with  the  adjacent  spinal  nerve.  Have  the 
assistant  help  you  find  the  sympathetic  strands  and  ganglia  in  the  roof  of  the 
cisterna  magna,  alongside  the  dorsal  aorta. 

8.  Sense  organs. — The  principal  sense  organs,  the  olfactory  sacs,  the  eyes, 
and  the  ears,  have  already  been  noted.     In  addition  there  are  sense  organs  in  the 
skin,  which  are  sensitive  to  touch,  light,  chemicals,  and  differences  of  temperature, 
and  taste  organs  in  the  lining  membrane  of  the  mouth. 


GENERAL  SURVEY  OF  THE  FROG  13 

Draw  a  diagrammatic  cross-section  through  the  frog  at  the  level  of  the 
stomach.  This  diagram  must  include  the  skin,  the  subcutaneous  lymph  spaces, 
the  vertebral  column  and  contained  spinal  cord,  the  cisterna  magna  and  its 
contents,  the  stomach,  duodenum,  pancreas,  tips  of  the  lobes  of  the  liver,  repro- 
ductive organs  and  their  ducts,  and  the  relation  of  the  peritoneum  and  the  mesenteries 
to  these  organs.  This  drawing  is  to  be  constructed  from  the  knowledge  gained 
from  the  foregoing  examination  of  the  frog.  Holmes,  Fig.  12,  may  be  consulted 
but  is  not  to  be  copied. 

The  general  anatomical  features  and  relations  expressed  in  such  a  diagram 
are  those  common  to  all  vertebrates  (except  the  subcutaneous  lymph  sacs). 
The  general  systems  of  organs  are  common  to  all  animals  except  the  lowest, 
although  the  details  vary  considerably. 


II.     GENERAL  PHYSIOLOGY 

In  the  preceding  section  a  general  survey  of  the  systems  of  organs  which 
make  up  the  structure  or  morphology  of  an  animal  has  been  made.  We  may 
next  logically  consider  the  functions  or  physiology  of  these  organs,  using,  as 
before,  the  frog  merely  as  an  example  to  illustrate  phenomena  which  are  common 
to  all  animals. 

A.      FUNCTION   OF  THE   NERVOUS   SYSTEM;     IRRITABILITY,    CONDUCTIVITY 

Irritability  is  the  capacity  of  living  matter  to  undergo  a  change  as  a  con- 
sequence of  changes  external  or  internal  to  itself.  The  change  in  the  living 
organism  is  known  as  the  reaction  or  response,  and  in  the  case  of  animals  the 
response  generally  becomes  visible  as  a  movement.  The  change  which  produces 
the  response  is  the  stimulus;  the  act  of  applying  a  stimulus  to  an  organism  is 
stimulation.  When  the  response  appears  at  a  different  point  than  that  to  which 
the  stimulus  was  applied,  it  is  quite  obvious  that  conduction  of  the  stimulus 
has  occurred,  and  this  capacity  of  living  substance  to  transmit  stimuli  is  known 
as  conductivity.  The  time  which  elapses  between  the  application  of  the  stimulus 
and  the  visible  response  is  called  the  reaction  time,  and  is  evidently  dependent 
upon  conductivity.  The  nervous  system  is  the  irritable  and  conductile  system 
par  excellence  of  the  body. 

Obtain  from  the  assistant  a  frog  pithed  in  the  brain  only  (why?).  Suspend 
it  by  a  wire  through  the  lower  jaw  from  the  crosspieces  of  the  electric  lights. 
Wait  until  it  hangs  quietly.  Have  a  pan  or  dish  of  tap  water  handy  to  keep  the 
frog  moist  and  to  wash  off  the  acid  in  the  following  experiment.  Do  not  allow 
the  frog  to  become  dry.  Dip  a  very  small  piece  of  filter  paper,  not  more  than  2  mm. 
square,  into  dilute  acetic  acid  and  stick  it  to  the  skin  of  the  abdomen  of  the  frog. 
Response?  Determine  with  a  watch  the  approximate  reaction  time.  Wash 
off  the  acid  with  water  and  repeat  in  various  ways,  putting  the  acid  on  the  toes, 
skin  of  the  hind  legs,  back,  etc.  Which  part  of  the  body  is  the  most  sensitive, 
as  determined  by  the  reaction  time?  When  are  the  fore  legs  used?  Does  the 
reaction  appear  to  be  intelligent  ?  Under  the  conditions  of  the  experiment  can 
it  be  so?  Read  Holmes,  pp.  300-2.  Such  a  reaction  is  called  a  reflex,  and  this 
particular  one  is  known  as  the  "wiping  reflex."  The  complete  path  involved  in 
such  a  reflex  can  be  understood  only  after  a  more  detailed  study  of  the  nervous 
system.  The  steps  involved  are:  stimulation  of  the  sense  organs  in  the  skin 
by  the  acid;  conduction  of  the  stimulation  along  the  spinal  nerves  leading  from 
these  sense  organs  to  the  spinal  cord;  conduction  in  the  spinal  cord  to  a  level 

14 


GENERAL  PHYSIOLOGY  , 

where  the  nerves  to  the  muscles  of  the  hind  legs  originate;  an  impulse  from  this 
level  of  the  cord  along  the  nerves  in  question  to  the  particular  muscles  needed , 
contraction  of  these  muscles  producing  movements  of  the  hind  legs. 

In  this  and  all  subsequent  experiments,  make  careful  observations  and  take- 
notes  on  what  happens  and  write  up  the  experiment  later  in  your  notebook, 
according  to  the  plan  suggested  in  the  introduction. 

B.      FUNCTION   OF   THE   MUSCULAR   SYSTEM;     CONTRACTILITY 

Contractility  is  the  capacity  of  living  matter  to  shorten  itself.  It  is  probable 
that  all  kinds  of  movements  in  animals  are  due  to  this  property,  which  is  par- 
ticularly specialized  in  the  muscles. 

1.  Contractility  of  voluntary  muscle  (muscle  under  control  of  the  will).— 
Remove  the  hook  from  the  frog's  jaw  and  now  pith  the  spinal  cord  (4).    Lay 
the  frog  back  upward,  make  a  circular  incision  through  the  skin  completely 
around  the  base  of  the  thigh,  and  grasping  the  cut  edge  of  the  skin,  completely 
strip  the  skin  from  the  hind  leg.     On  the  dorsal  side  of  the  thigh,  three  muscles 
will  be  seen:   laterally,  the  glutaeus  magnus;   medially,  the  semimembranosus; 
and  between  them  the  small  slender  ileo-fibularis.     On  the  back  of  the  shank  is 
a  large  spindle-shaped  muscle,  the  gastrocnemius.     Carefully  separate  the  ileo- 
fibularis  from  the  semimembranosus  and  locate  between  them  the  sciatic  nerve, 
appearing  as  a  stout,  white  cord  running  alongside  of  a  dark-colored  blood  vessel. 
Carefully  isolate  the  nerve  from  the  blood  vessel,  handling  it  with  the  utmost 
care.     Lift  it  up  and  while  watching  the  gastrocnemius  muscle  cut  through  the 
nerve.     What  happens?     What  is  the  stimulus?     How  does  the  stimulus  get 
to  the  muscle?     How  does  the  reaction  time  compare  with  that  in  the  preceding 
experiment?     Why?     The  experiment  may  be  repeated  as  many  times  as  desired 
by  again  cutting  the  nerve  between  the  first  cut  and  the  muscle.     Satisfy  your- 
self that  hi  the  motion  the  muscle  actually  becomes  shorter  and  thicker,  and  that 
this  change  in  its  shape  is  the  cause  of  the  movement. 

2.  Contractility  of  involuntary  muscle  (muscle  not  under  control  of  the  will, 
found  mainly  in  the  walls  of  the  digestive  tract). — Turn  the  frog  ventral  side 
upward  and  cut  through  the  ventral  body  wall  to  the  left  of  the  median  line  from 
the  pelvic  girdle  up  through  the  pectoral  girdle.     Gently  pull  the  stomach  out 
so  that  it  will  be  clearly  exposed  and  with  a  forceps  pinch  the  wall  of  the  stomach. 
Wait  for  the  response.     How  does  the  reaction  time  compare  with  that  of  volun- 
tary muscle  ?     Watch  the  contraction  travel.     In  which  direction  does  it  go  ? 
This  kind  of  contraction  is  called  peristalsis.     What  is  its  purpose? 

3.  Contractility  of  heart  muscle. — Free  the  heart  carefully  from  the  peri- 
cardial  sac  and  observe  that  the  beating  of  the  heart  is  nothing  but  a  rhythmical 
contraction  of  its  muscular  walls.     In  what  order  do  the  parts  of  the  heart  beat ? 
Observe  changes  in  color,  form,  and  size  of  the  auricles  and  ventricle  during 


16  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

contraction.  Turn  the  heart  with  the  apex  forward  so  that  the  sinus  venosus 
can  be  seen.  Does  the  sinus  beat?  What  time  relation  does  its  beat  bear  to 
that  of  the  auricles  and  ventricle? 

Count  and  record  the  number  of  heart  beats  per  minute.  Then  cool  the 
heart  by  placing  small  pieces  of  ice  around  it,  and  after  it  has  become  thoroughly 
chilled  again  count  the  rate  of  the  heart  beats.  This  illustrates  in  a  striking  way 
the  effect  of  change  of  temperature  on  the  activities  of  living  matter. 

4.  Ciliary  motion. — Open  the  mouth  of  the  frog,  swab  it  out  with  water,  and 
if  necessary  cut  the  angle  of  the  jaws  to  keep  it  open.     Lay  the  frog  ventral 
side  up  and  sprinkle  a  little  powdered  carmine  or  place  small  bits  of  cork  on  the 
posterior  part  of  the  roof  of  the  mouth.     Observe  that  the  particles  travel  as 
if  carried  on  a  current.     (If  the  experiment  fails  it  is  because  the  frog  has  been 
pithed  too  long,  and  a  fresh  frog  may  be  necessary.)     The  current  is  due  to  a 
multitude  of  microscopic  hairlike  processes,  called  cilia,  which  cover  the  roof 
of  the  mouth,  and  by  their  co-ordinated  beating  produce  a  current  of  mucus 
which  is  sufficiently  strong  to  carry  fairly  large  particles.     Prove  that  the  particles 
will  be  transported  against  the  force  of  gravity  by  repeating  the  experiment  with 
the  head  of  the  frog  tilted  at  an  angle,  so  that  the  particles  must  be  carried  uphill. 
In  which  direction  does  the  ciliary  current  run  and  what  is  its  purpose?    While 
the  causes  of  ciliary  motion  are  not  at  all  understood,  it  is  probable  that  like 
muscular  movement  it  is  a  form  of  contractility. 

5.  Amoeboid  movement. — In  this  type  of  movement,  which  is  limited  tc 
very  small  or  microscopic  masses  of  living  matter,  locomotion  is  accomplished 
by  the  flowing  out  of  portions  of  living  substance  into  processes.     The  remainder 
of  the  substance  then  flows  into  the  processes,  new  processes  are  put  out,  and  a 
slow  change  of  position  is  thus  effected.     Amoeboid  movement  is  probably  the 
most  simple  form  of  contractility,  but  an  adequate  analysis  of  its  causes  has  not 
yet  been  made. 

Amoeboid  movement  is  illustrated  in  the  frog  in  the  black  chromatophores 
or  color  bodies  of  the  skin,  and  in  the  white  blood  corpuscles,  both  of  which  objects 
will  be  seen  later.  For  the  present  see  Holmes  (Fig.  49,  p.  189,  and  Fig.  71, 
p.  259),  as  neither  of  them  is  very  favorable  for  the  study  of  this  kind  of  move- 
ment. Amoeboid  movement  will  be  studied  in  the  amoeba,  the  animal  from 
which  the  movement  takes  its  name. 


C.      FUNCTION  OF  THE  DIGESTIVE   SYSTEM;    DIGESTION,   ABSORPTION 

The  food  of  animals  in  general  consists  of  water,  salts,  and  organic  substances, 
these  latter  being  divided  into  three  classes,  proteins,  carbohydrates,  and  fats. 
Examples  of  proteins  are  meat,  white  of  egg,  curdle  of  milk,  blood  clot;  sugars 
and  starches  are  carbohydrates;  butter,  fat  of  meat,  cream,  are  examples  of  fats. 
While  the  water  and  salts  pass  into  the  substance  of  the  animal  without  alter  a- 


GENERAL  PHYSIOLOGY  I? 

tion,  the  carbohydrates,  fats,  and  proteins  are  too  complex  to  be  absorbed  and 
used  by  the  animal,  and  must  be  broken  down  into  simpler  substances  before 
they  can  be  utilized.  The  splitting  of  these  organic  foods  into  simpler,  utilizable 
substances  is  the  process  of  digestion,  and  the  performance  of  this  process  is  the 
function  of  the  alimentary  tract  and  its  glands.  Digestion  is  brought  about 
by  means  of  certain  substances,  called  enzymes,  which  are  manufactured  in  the 
walls  of  the  alimentary  tract  and  in  the  digestive  glands,  chiefly  the  pancreas. 
By  means  of  these  enzymes,  organisms  are  able  to  produce  chemical  changes  in 
foods  which  cannot  be  imitated  in  the  laboratory  at  all  or  which  can  be  imitated 
only  by  the  use  of  boiling  temperatures  and  reagents  which  would  be  fatal  to 
life.  Neither  the  chemical  nature  of  enzymes  nor  the  mode  of  their  action  is 
known,  but  it  is  probable  that  they  attach  themselves  either  physically  or 
chemically  to  the  molecules  of  the  substance  upon  which  they  act,  thus  upsetting 
the  equilibrium  within  the  molecule,  and  causing  it  to  fall  into  fragments, 
whereupon  the  enzyme  is  set  free  again  unchanged.  In  general  each  enzyme 
is  capable  of  acting  upon  only  one  substance  or  class  of  substances.  Thus, 
enzymes  which  split  up  proteins  are  called  proteases;  those  which  split  starches 
and  sugars  are  diastases;  and  those  which  split  fats  are  Upases  (see  Holmes, 
chap,  vii,  pp.  i34~38>  *42,  156,  163). 

In  the  following  experiments,  the  action  of  each  of  these  three  general  kinds 
of  enzymes  is  demonstrated.  As  it  is  rather  impractical  to  obtain  enzymes  from 
the  frog,  human  and  pig  enzymes  having  the  same  action  are  used  instead. 

1.  Action  of  a  protease — pepsin. — 

a)  The  gastric  juice:  This  digestive  fluid  is  secreted  by  glands  located  in  the 
wall  of  the  stomach.     It  contains  about  o .  4  per  cent  hydrochloric  acid,  an  enzyme 
called  pepsin,  and  a  number  of  salts.    An  "artificial"  gastric  juice  is  readily 
made  by  adding  0.4  per  cent  hydrochloric  acid  to  commercial  dried  pepsin,  gen- 
erally obtained  from  the  hog's  stomach. 

b)  Action  of  pepsin:    Into  a  test  tube  put  5-10  c.c.  of  artificial  gastric  juice, 
and  into  another  5-10  c.c.  of  o .  4  per  cent  hydrochloric  acid.    Add  to  each  a  small 
quantity  of  boiled  white  of  egg,  cut  into  very  small  pieces.    Place  in  a  water  bath 
or  incubator  kept  at  37°  C.  (why?)  for  at  least  two  hours.    What  becomes  of  the 
protein?    Is  the  acid  alone  without  the  pepsin  capable  of  producing  this  effect? 
Pepsin  from  the  frog's  stomach  has  the  same  action  (Holmes,  p.  142). 

2.  Action  of  a  lipase — pancreatic  lipase. — 

a)  Reaction  of  milk :  To  10  c.c.  of  milk  in  a  test  tube  add  a  few  drops  of  neutral 
litmus  solution,  or  test  with  red  and  blue  litmus  paper.    Litmus  is  a  vegetable 
dye,  which  is  pink  in  acid  solution,  blue  in  alkaline  solution,  and  purplish  in 
neutral  solution.     Is  milk  acid,  alkaline,  or  neutral? 

b)  Action  of  pancreatic  lipase:    A  solution  of  this  enzyme  is  obtained  by 
dissolving  dried  pancreas,  sold  commercially  as  pancreatin,  in  a  slightly  alkaline 
solution.     Add  a  few  cubic  centimeters  of  this  solution  to  the  litmus-containing 


18  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

milk  prepared  in  (a).  What  color  is  the  mixture?  Keep  in  the  water  bath  at 
37°  C.,  and  observe  from  time  to  time.  Does  the  color  change?  What  does  this 
indicate?  The  action  is  of  course  upon  the  cream  (fat)  of  the  milk  (Holmes, 
p.  151).  (R,  L,  A.)  A  similar  lipase  is  secreted  by  the  pancreas  of  the  frog. 

3.  Action  of  a  diastase — ptyalin. — 

a)  Test  for  starch:  Place  a  few  cubic  centimeters  of  a  i  per  cent  starch  paste 
in  a  test  tube  and  add  a  drop  or  two  of  iodine  solution.    A  deep  blue  color  results, 
which  proves  the  presence  of  starch.     The  nature  of  this  blue  compound  which 
iodine  forms  with  starch  is  unknown. 

b)  Test  for  sugar:  Place  a  few  cubic  centimeters  of  glucose  (fruit  sugar)  solu- 
tion in  a  test  tube,  add  a  few  drops  of  Fehling's  solution,  and  heat  to  boiling.     A 
yellow,  greenish,  or  red  precipitate  proves  the  presence  of  sugar. 

c)  Test  the  starch  paste  with  Fehling's  solution.     Is  any  sugar  present  in  it? 

d)  Test  some  saliva,  spit  out  from  your  mouth,  with  Fehling's  solution.    Does 
it  contain  any  sugar? 

e)  Action  of  saliva:  Put  about  5  c.c.  of  the  starch  paste  in  a  test  tube,  and 
spit  some  saliva  from  the  mouth  into  it.     Shake  up  thoroughly  and  place  in  the 
water  bath  at  37°  C.  for  several  minutes.     Remove  and  test  with  Fehling's  solu- 
tion.    Is  sugar  present?     Where  did  it  come  from?    The  enzyme  in  the  saliva 
which  has  this  action  is  called  ptyalin  (from  a  Greek  word  meaning  "spit").     An 
enzyme  having  a  similar  action  is  secreted  by  the  pancreas  of  the  frog  (the  mouth 
secretions  of  the  frog  have  no  digestive  action). 

Explain  fully  in  your  notebook  the  action  of  these  enzymes.  State  your 
observations  and  interpret  them.  Consult  Holmes,  pp.  136-37,  142,  151.  A 
general  textbook  of  physiology,  obtainable  in  the  library,  will  also  be  helpful. 

4.  Absorption. — This  is  the  process  by  means  of  which  the  products  of  diges- 
tion are  transferred  through  the  wall  of  the  intestine  into  the  blood  and  lymph 
vessels  for  transport  to  all  parts  of  the  body.     The  process  is  impractical  of 
demonstration  in  the  frog. 


D.      FUNCTION  OF  THE  RESPIRATORY   SYSTEM;    RESPIRATION,   OXIDATION 

When  any  organic  material  burns,  it  uses  up  oxygen  from  the  air  and  gives  off 
carbon  dioxide.  In  exactly  the  same  way  living  substance  burns  either  itself 
or  the  materials  which  it  obtains  from  digestion,  using  up  oxygen  and  releasing 
carbon  dioxide.  All  of  the  processes  involved  in  this  burning  are  called  collec- 
tively respiration. 

i.  External  respiration  in  the  frog. — The  process  and  mechanisms  involved 
in  getting  the  oxygen  of  the  air  into  the  body  and  throwing  out  the  carbon  dioxide 
constitute  external  respiration.  Obtain  a  live  frog,  place  it  in  a  covered  dish 
with  a  small  amount  of  water,  and  after  it  has  become  quiet  study  the  respiratory 
movements.  These  consist  of  the  opening  and  closure  of  the  external  nares, 


GENERAL  PHYSIOLOGY  Ig 

rise  and  fall  of  the  floor  of  the  buccal  cavity,  and  contraction  and  expansion  of 
the  sides  of  the  body.  Time  the  rate  of  each  of  the  movements.  Can  you  discover 
any  correlation  between  any  of  these  movements?  Does  the  frog  respire  in  the 
same  manner  as  the  human  (R,  L,  A)?  Read  Holmes,  pp.  168-177,  understand 
thoroughly  the  mechanism  of  respiration  in  the  frog  and  write  an  account  of  it 
in  your  notebook. 

2.  Respiratory   activity   of   the   skin. — Demonstration   experiment.     Three 
jars,  each  containing  a  frog,  are  placed  in  a  trough  of  running  water,  so  that  the 
temperature  of  all  is  the  same.     One  is  filled  with  running  water,  the  second  with 
standing  water,  so  that  all  bubbles  of  air  are  entirely  excluded,  and  the  third  has 
an  inch  or  two  of  water  in  the  bottom.     Do  the  frogs  immersed  in  water  show 
respiratory  movements?     How  do  they  get  oxygen?    What  is  the  condition  of 
the  three  frogs  after  two  or  three  days?     Explain  fully  in  your  notebook. 

3.  Carbon  dioxide  output. — The  following  simple  experiment  demonstrates 
that  carbon  dioxide  is  given  off  from  the  lungs.     (This  need  not  be  performed  by 
those  familiar  with  it.)     A  bottle  is  furnished  containing  two  or  three  inches  of 
lime  water  or  saturated  solution  of  barium  hydroxide,  and  provided  with  two 
tubes,  one  of  which  extends  below  the  lime  water  while  the  other  does  not.     First 
draw  atmospheric  air  through  the  lime  water  by  sucking  on  the  shorter  tube. 
Does  atmospheric  air  contain  enough  carbon  dioxide  to  produce  a  precipitate 
with  lime  water?     Then  blow  air  from  the  lungs  into  the  longer  tube.     What 
happens?     Explain  fully  (A). 

4.  Internal  respiration  or  oxidation. — The  respiratory  movements  considered 
in  sections  i  and  2  are  merely  methods  for  getting  the  oxygen  into  the  body  and 
into  the  blood.     The  actual  use  of  the  oxygen  by  the  living  substance  of  the 
animal  is  the  real  process  of  respiration.     To  avoid  confusion,  this  process  is 
designated  as  internal  respiration,  or  oxidation. 

E.      FUNCTION   OF  THE  EXCRETORY  SYSTEM;    EXCRETION 

Every  part  of  the  organism  as  the  result  of  its  activities  gives  off  waste 
matters.  Those  derived  from  the  oxidation  of  fats  and  carbohydrates  are  mainly 
carbon  dioxide  and  water,  which  are  cast  off  through  the  lungs  and  skin.  Those 
derived  from  the  oxidation  of  proteins,  or  other  chemical  splittings  of  proteins, 
contain  nitrogen,  and  these  nitrogenous  wastes  are  taken  from  the  blood  and 
lymph  by  the  kidneys  and  eliminated  from  the  body.  This  function  of  the 
kidneys  is  called  excretion.  The  student  should  note  that  excretion  is  an  active 
process,  which  is  concerned  with  the  elimination  of  soluble  materials  which  have 
once  been  a  part  of  the  body;  therefore  the  purely  passive  ejection  of  undigestible 
materials  from  the  intestine  is  NOT  excretion,  and  should  not  be  confused  with  that 
process,  as  students  are  prone  to  do.  Such  undigested  food  in  the  intestine  is 
designated  as  feces,  and  its  passage  from  the  body  is  the  process  of  defecation 
or  egestion. 


20  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

F.      FUNCTION   OF   THE    CIRCULATORY   SYSTEM;     CIRCULATION   OF   THE   BLOOD 

The  food  prepared  in  the  digestive  tract  and  the  oxygen  taken  in  through 
the  lungs  must  be  carried  to  all  parts  of  the  body;  and  the  waste  materials  from 
these  parts  conveyed  to  the  kidneys  and  lungs.  Such  transport  of  materials  is 
the  function  of  the  circulatory  system. 

Demonstration  of  the  circulation  of  the  blood.  In  the  web  of  the  frog's 
hind  foot,  spread  out  under  the  microscope,  observe  the  following: 

1.  The  network  of  tubes,  the  blood  vessels,  in  which  the  blood  flows. 

2.  The  composition  of  the  blood. — It  consists  of  solid  bodies,  the  corpuscles, 
which  may  be  seen  shooting  along  the  vessels,  and  the  colorless  fluid,  the  plasma, 
in  which  they  are  suspended. 

3.  The  arteries,  vessels  in  which  the  blood  flows  from  the  larger  vessels  into 
their  smaller  branches. 

4.  The  veins,  vessels  in  which  the  blood  flows  from  the  smaller  into  the 
larger  vessels. 

5.  The  capillaries,  the  smallest  vessels,  forming  a  network,  in  which  the 
direction  of  flow  is  indefinite. 

6.  The  pulse,  rhythmic  jerks  in  the  blood  stream,  due  to  the  heart  beats, 
observable  only  in  the  arteries. 

7.  The  chromatophores,  the  small  black  bodies  in  the  skin.    They  may 
exhibit  various  shapes.    In  the  contracted  state,  they  are  round  black  masses; 
in  the  expanded  state,  they  show  long,  delicate,  spidery  processes. 

G.      FUNCTION  OF  THE  REPRODUCTIVE   SYSTEM;    REPRODUCTION, 
DEVELOPMENT,   THE  LIFE-CYCLE 

The  ovaries  produce  the  female  elements,  which  are  called  eggs  or  ova,  and 
the  testes  produce  the  male  elements,  which  are  called  spermatozoa.  Before  the 
egg  can  develop  it  must  unite  with  a  single  spermatozoon,  a  process  known  as 
fertilization.  The  fertilized  egg  then  undergoes  a  process  of  development  which 
results  in  the  production  of  an  individual  like  the  one  from  which  the  egg  arose. 
The  complete  history  from  one  individual  to  the  next  is  called  ontogeny,  or  the 
life-cycle.  As  the  life-cycle  of  the  frog  occupies  too  great  a  period  of  time  for 
its  completion,  the  life-cycle  of  an  insect  will  be  studied  instead.  For  this  pur- 
pose either  the  small  fruit  fly  (Drosophila)  or  the  common  blowfly  may  be  used. 
The  latter  is  preferable  owing  to  its  larger  size  but  is  available  only  during  the 
warm  months.  If  Drosophila  is  to  be  used,  each  table  will  be  given  a  bottle 
containing  a  pair  of  fruit  flies  and  a  piece  of  banana  as  food.  If  blowflies  are 
to  be  used,  a  bottle  will  be  provided  containing  two  or  three  inches  of  moist  sand; 
put  a  piece  of  liver  in  it  and  set  it  near  an  open  window.  Watch  the  gathering 
of  flies  about  the  bottle  and  observe,  if  you  have  time,  the  laying  of  eggs  upon  the 
liver  by  the  female  flies.  Then  stopper  the  bottle  with  a  wad  of  cotton. 


GENERAL  PHYSIOLOGY  2I 

1.  The  flies. — Obtain  a  Drosophila  killed  by  ether  and  note  its  character- 
istic insect  structure;  the  division  of  the  body  into  head,  thorax,  and  abdomen, 
the  characteristic  rings  or  segments  of  which  the  abdomen  is  formed,  the  large 
eyes,  three  pairs  of  legs,  and  single  pair  of  wings  (most  insects  have  two  pairs  of 
wings,  but  flies  are  characterized  by  one  pair).     Learn  to  distinguish  male  and 
female  fruit  flies  (A).    The  males  have  slender  rounded  abdomens  with  a  black 
area  in  the  middle  of  the  tip  of  the  ventral  side;  the  females  have  broader,  more 
pointed  abdomens,  and  the  black  markings  are  at  the  sides  of  the  ventral  surface 
of  the  abdomen.     In  male  blowflies,  the  large  eyes  nearly  meet  in  front  while 
in  the  females  there  is  a  considerable  distance  between  them.     (If  the  experiment 
on  heredity  is  to  be  performed,  the  two  fruit  flies  given  you  will  differ  from  each 
other  in  some  striking  way.) 

2.  The  eggs. — Note  and  record  the  date  on  which  the  eggs  are  first  observed. 
They  are  oval  white  objects,  minute  in  the  case  of  the  fruit  fly,  much  larger  in 
the  blowfly.     Remove  one  and  study  under  the  low  power  of  the  microscope. 
Read  carefully  the  directions  regarding  the  use  of  the  microscope,  and  consult 
the  assistant  on  any  points  that  you  do  not  understand.    The  egg  of  the  fruit 
fly  has  hexagonal  sculpturings  upon  the  surface  which  are  said  to  be  the  impres- 
sions of  the  walls  of  the  oviducts,  and  is  provided  with  two  oarlike  processes 
which  prevent  the  egg  from  sinking  into  the  soft  banana  pulp,  a  circumstance 
which  would  probably  be  fatal  to  the  larva  when  it  emerges.    The  egg  of  the 
blow  fly  is  marked  similarly  but  less  conspicuously  with  hexagons,  has  a  concave 
surface  which  is  the  future  dorsal  side,  and  a  convex  surface  which  is  ventral. 
Draw  an  egg  of  either  fly. 

3.  The  larvae.— Note  and  record  the  date  on  which  the  moving,  wormlike 
larvae  are  first  noticed.     The  larva  develops  inside  the  eggshell,  and  hatches 
forth  rather  suddenly  by  rupture  of  this  shell.     Remove  a  larva  to  a  slide, 
anaesthetize  with  ether  with  the  aid  of  the  assistant,  cover  with  a  cover  glass, 
and  study  under  the  low  power  of  the  microscope.     Compare  its  structure  with 
that  of  the  parent  fly.     Is  it  more  simple?    Does  it  have  head,  eyes,  wings,  legs? 
Is  the  body  divided  into  regions?    Is  the  segmentation,  or  ringing  of  the  body, 
more  marked  than  in  the  parent?    What  animals  do  you  know  that  are  similarly 
ringed  along  their  entire  bodies?    The  significance  of  these  facts  may  not  yet 
be  clear  to  the  student,  but  they  illustrate  one  of  the  most  fundamental  and 
general  laws  of  development,  that  every  organism  in  its  development  passed 
through  stages  simpler  than  itself,  and  stages  that  resemble  animals  lower  in 
the  scale  of  animal  life  than  itself. 

,  The  most  striking  structure  observable  in  the  larva  are  the  tracheal  tubes, 
consisting  of  a  pair  of  longitudinal  trunks  running  the  length  of  the  body,  ending 
posteriorly  in  a  pair  of  large  openings,  anteriorly  in  a  pair  of  smaller  ones,  and 
sending  off  extensive  branches  throughout  the  body.  These  tubes  are  full  of 
air  which  enters  them  through  the  openings,  called  spiracles,  and  through  their 


22  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

minute  branches  is  conveyed  to  all  parts  of  the  body.  The  respiratory  system 
of  air  tubes  is  found  only  in  insects  and  their  near  relatives  and  differs  from  that 
of  other  animals  where  the  oxygen  is  carried  by  the  blood.  The  anterior  pro- 
trusible  end  of  the  larva  is  a  very  imperfect  head,  with  a  mouth  leading  into  a 
pharynx  which  is  provided  with  hard,  black,  curiously  shaped  jaws.  These  can 
readily  be  seen  with  the  naked  eye  in  the  living  larva  and  their  action  in  taking 
in  the  soft  food  should  be  noted.  Each  segment  of  the  larva  is  encircled  with 
a  ring  of  many  small  pointed  teeth  used  to  prevent  slipping.  The  body  of  the 
larva  is  filled  mainly  by  the  digestive  tract,  which  is  much  coiled  and  folded,  and 
by  the  yellowish  fat  bodies,  in  which  the  excessive  food  taken  in  by  the  larva  is 
stored  up  to  be  used  for  the  next  stage  in  development.  In  the  blowfly  larvae, 
especially  when  they  have  become  pretty  large,  there  may  be  seen  with  the 
naked  eye  a  sac,  the  food  reservoir,  an  outgrowth  of  the  esophagus,  filled  with 
the  reddish  liver  which  has  been  devoured.  Make  a  drawing  of  the  larva. 

Note  the  remarkably  rapid  increase  in  size,  or  growth,  of  the  larva.  In  growth 
the  non-living  food  is  transformed  into  the  living  substance  of  the  organism 
(process  of  assimilation).  What  use  do  the  blowfly  larvae  make  of  the  sand? 
Which  side  of  the  meat  do  they  frequent  and  why? 

4.  The  pupae. — Record  the  date  on  which  the  motionless  brown  pupae  are 
first  observed.     The  larvae,  when  fully  grown,  cease  to  feed,  become  motionless, 
and  shrink,  leaving  their  skins  to  form  the  brown  pupal  cases.     Within  this  case, 
the  adult  fly  develops  from  certain  rudiments  present  in  the  larva,  while  most 
of  the  larval  structure  disintegrates  and  serves  as  food  material  for  the  developing 
adult.    As  time  passes  observe  the  adult  structures  appearing  within  the  pupal 
case,  the  most  conspicuous  being  the  eyes  and  wings.     Remove  a  pupa,  examine 
under  the  low  power  and  sketch.     Is  it  segmented?     In  Drosophila  the  two 
prominent  processes  at  the  anterior  end  and  the  less  conspicuous  ones  at  the 
posterior  end  are  the  same  spiracular  openings  noticed  in  the  larva,  and  serve 
to  admit  air  to  the  tracheal  system.    The  pupa  of  the  blowfly  has  no  such 
projections,  but  the  posterior  end  has  a  number  of  short  spines  of  no  evident 
function. 

5.  The  adults  (imagines). — Record  the  date  on  which  adult  flies  are  first 
noted.     Observe  that  the  pupal  case  is  ruptured  and  left  behind  by  the  fly. 
How  many  days  were  required  for  the  entire  life-cycle?    Would  the  time  be  the 
same  for  all  periods  of  the  year?    How  many  flies  were  produced?    Proportion 
of  males  and  females?     If  all  the  offspring  lived  to  produce  at  the  same  rate, 
how  many  would  there  be  at  the  end  of  three  months?    What  factors  in  nature 
prevent  this  enormous  increase  in  numbers? 

The  life-cycle  of  a  fly  is  a  typical  insect  life-cycle.  A  sudden  transformation 
in  life-cycle,  such  as  that  from  the  larva  to  the  adult,  is  called  a  metamorphosis. 
The  transformation  of  the  tadpole  (polliwog)  into  the  frog  is  another  example  of 
metamorphosis.  On  the  other  hand,  many  animals  have  no  such  sudden  meta- 


GENERAL  PHYSIOLOGY  2^ 

morphoses  in  their  life-histories,  but  the  development  is  slow  and  gradual.  From 
what  you  have  learned  in  this  experiment,  do  you  think  that  flies  grow?  Are 
small  flies  the  young  of  larger  flies? 

H.      SUMMARY  OF  PHYSIOLOGICAL  PROCESSES 

1.  Food  prepared  in  the  digestive  tract  by  the  action  of  enzymes  is  absorbed 
through  the  walls  of  the  intestine  into  the  circulatory  system. 

2.  Oxygen  drawn  into  the  lungs  through  the  mechanical  arrangement  of  the 
respiratory  system  passes  through  the  walls  of  the  lungs  or  through  the  skin  into 
the  circulatory  system. 

3.  The  circulatory  system  transports  food  and  oxygen  to  all  parts. 

4.  The  living  substance  of  the  body  withdraws  the  food  and  oxygen  from  the 
lymph  and  blood,  and  uses  them: 

a)  For  the  formation  of  new  chemical  compounds  or  of  new  living  substance 
(process  of  assimilation),  thus  accomplishing  growth. 

b)  For  the  production  of  energy,  by  burning  the  food  material  with  the  aid 
of  the  oxygen  (process  of  oxidation).     The  living  substance  itself  may  also  be 
burned  and  produce  energy. 

5.  The  waste  products  resulting  from  the  oxidation  are  excreted  into  the 
blood  which  carries  them  to  the  lungs,  skin,  and  kidneys,  where  they  are  thrown 
out  from  the  body.    The  lungs  excrete  mainly  carbon  dioxide  and  water;   the 
skin,  carbon  dioxide,  water,  and    dissolved  waste  matters;    and  the  kidneys, 
dissolved  nitrogenous  waste  materials. 

6.  The  combined  processes  of  assimilation,  oxidation   (or  other  energy- 
producing  changes),  and  excretion  are  spoken  of  together  as  metabolism.    Metab- 
olism may  be  defined  as  the  sum  of  those  chemical  changes  taking  place  in 
protoplasm  which  result  in  the  production  of  new  compounds,  new  protoplasm, 
or  of  energy. 

7.  The  energy  produced  in  the  metabolic  processes  is  utilized  to  carry  on 
the  activities  of  the  body,  for  the  contraction  of  muscles,  conduction  of  nerve 
impulses,  secretion  of  digestive  fluids,  etc. 


m.     GENERAL  HISTOLOGY:    CELLS  AND  TISSUES 

The  protoplasm  of  which  living  bodies  are  composed  does  not  exist  as  a  con- 
tinuous mass,  but  is  divided  up  into  minute  portions,  each  of  which  is  called  a 
cell.  A  cell  is  defined  as  a  small  mass  of  protoplasm,  containing  a  differentiated 
body,  the  nucleus.  All  organisms  are  either  composed  of  a  number  of  cells  or 
consist  of  a  single  cell.  That  branch  of  biology  which  devotes  itself  to  the 
detailed  study  of  the  different  kinds  of  cells  which  occur  in  living  things  is  called 
histology ',  and  that  part  of  histology  which  is  concerned  with  the  structure  of  the 
protoplasm  hi  different  kinds  of  cells  is  sometimes  distinguished  as  cytology. 

As  most  cells  are  of  minute  size,  the  microscope  is  necessary  for  their  study. 
Read  carefully  the  sheet  of  instructions  regarding  the  use  of  the  microscope, 
and  consult  the  assistants  on  any  points  which  you  do  not  understand.  Do  not 
fail  to  heed  the  directions  regarding  adjustment  of  the  light  and  use  of  the  adjust- 
ment screws.  Set  up  your  microscope  ready  for  use,  take  from  your  box  of 
slides  the  slide  labeled  "Necturus — liver,"  and  practice  with  this  slide  until  you 
are  familiar  with  the  method  of  operation  of  the  instrument. 

NOTE. — -As  students  frequently  exhibit  curiosity  about  the  preparation  of 
microscopic  slides,  such  as  are  to  be  used  in  this  section  of  the  work,  a  word 
about  this  process  may  be  introduced  here.  The  piece  of  material  of  which 
slides  are  desired  is  removed  from  a  freshly  killed  animal,  placed  in  a  fluid  which 
Hlls  it  and  preserves  it  in  a  nearly  natural  condition,  hardened  and  dehydrated 
in  alcohols  of  increasing  concentration,  and  imbedded  in  some  substance  such 
as  paraffin,  which  can  be  obtained  in  both  liquid  and  solid  condition.  The 
paraffin  containing  the  object  is  then  hardened  in  a  cold  medium,  cut  into  a 
rectangular  shape  and  mounted  on  a  machine  called  a  microtome.  In  the 
microtome  the  paraffin  block  is  moved  up  and  down  by  means  of  an  automatic 
micrometer  screw  across  a  very  sharp  knife  edge,  which  slices  off  exceedingly 
thin  sections  of  the  material  which  is  imbedded  in  the  paraffin.  Each  such  slice 
is  called  a  section,  and  when  these  sections  are  mounted  on  the  slide  in  the  order 
in  which  they  are  cut,  they  are  called  serial  sections.  While  such  sections  may 
be  cut  as  thin  as  nnnr  of  a  millimeter,  they  are  generally  about  y-J-g-  of  a  milli- 
meter. After  the  sections  are  mounted  on  the  slide  in  such  a  way  that  they 
stick  tightly,  the  paraffin  is  dissolved,  and  the  piece  of  material  is  then  stained 
(in  order  to  make  the  structures  clearer)  by  dyes  which  are  similar  to  those  used 
in  dyeing  cloth.  Finally  the  sections  are  covered  with  a  cover  glass  with  the 
aid  of  some  medium  which  cannot  dry  up. 

24 


GENERAL  HISTOLOGY:  CELLS  AND  TISSUES  25 

The  student  will  now  understand  that  owing  to  the  numerous  processes  and 
chemical  agents  to  which  the  material  is  subjected  in  the  making  of  a  slide, 
artificial  and  abnormal  appearances  are  frequently  produced.  Further,  a  differ- 
ence in  the  angle  at  which  the  material  is  sliced  will  make  two  slides  of  the  same 
material  present  a  different  appearance.  In  studying  slides,  the  student  must 
always  bear  these  points  in  mind,  and  should  direct  his  attention  only  to  those 
portions  of  the  sections  which  are  pronounced  by  the  assistant  to  be  typical  and 
normal,  and  illustrative  of  the  structures  under  consideration. 


A.      STUDY  OF  A  TYPICAL   CELL 

i.  Liver  cells  of  Necturus. — (Necturus  is  an  amphibian,  a  relative  of  the 
frog,  and  often  chosen  for  microscopic  preparations  because  its  cells  are  much 
larger  than  those  of  the  frog.)  Examine  with  the  low  power  the  slide  marked 
"  Necturus — liver"  and  note  that  the  liver  is  composed  of  polygonal  blocks.  Each 
of  the  blocks  is  a  cell,  and  we  thus  see  that  the  liver  is  made  up  of  such  cells. 
Inspection  of  all  parts  of  the  animal  would  show  that  they,  too,  are  similarly 
constructed. 

Turn  on  the  high  power  and  examine  the  structure  of  a  liver  cell  in  detail 
(Hegner,  pp.  26-29).  Note: 

a)  The  cell  wall,  or  cell  membrane,  the  delicate  partition  which  separates  each 
cell  from  its  neighbors.     In  many  cases,  the  cell  walls  may  not  be  as  distinct 
as  they  are  here. 

b)  The  nucleus,  the  spherical  deeply  stained  body  in  the  center  of  the  cell. 
A  membrane,  the  nuclear  membrane,  separates  the  nucleus  from  the  surrounding 
cytoplasm.    Within  the  nucleus  the  solid  material  takes  the  form  of  a  network, 
the  linin  network,  not  very  distinct  here,  on  the  fibers  of  which  are  strung  the 
conspicuous,  deeply  stained  irregular    masses,  the  chromatin  granules.     This 
chromatin  is  a  substance  characteristic  of  and  found  with  few  exceptions  only 
in  the  nucleus,  and  is  recognizable  by  its  staining  properties.     The  meshes  of 
the  linin  network  are  filled  with  a  clear,  transparent,  invisible  fluid,  called  the 
nuclear  sap,  the  nucleoplasm,  or  karyolymph. 

c)  The  cytoplasm,  the  portion  of  the  protoplasm  outside  of  the  nucleus.  It 
consists  of  a  mixture  of  solid  and  somewhat  fluid  materials;  the  fluid  portion  is 
transparent  and  is  known  as  the  ground  substance,  or  cell  sap,  or  hyaloplasm.  The 
solid  material  in  these  liver  cells  is  apt  to  appear  as  a  network,  the  apparent 
fibers  of  which  are  really  rows  of  granules.  This  network  in  the  cytoplasm  is 
called  the  spongioplasm,  and  was  formerly  thought  to  represent  the  real  structure 
of  the  cytoplasm;  but  it  is  now  believed  to  be  due  to  the  action  of  killing  fluids 
upon  the  protoplasm.  Besides  the  spongioplasmic  network,  the  cytoplasm 
frequently  contains  granules,  droplets,  fibers,  etc. 
Draw  a  cell  under  high  power,  showing  all  details. 


26  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

2.  Eggs  of  the  sea  urchin. — The  eggs  or  ova  of  all  animals  are  single  cells. 
Examine  with  the  low  power  the  slide  marked  "  Arbacia — mitosis"  and  note  on 
it  the  sections  of  the  eggs  of  the  sea  urchin  (Arbacia).  With  the  aid  of  the  assist- 
ant find  an  unfertilized  egg,  recognized  by  its  large,  clear  nucleus.  Examine 
under  the  high  power.  Note  the  very  large  nucleus,  containing  an  unusually 
large  amount  of  nuclear  sap,  the  chromatin  granules  in  the  nucleus,  the  large 
black  spot  in  the  nucleus,  called  the  nucleolus,  or  plasmosome;  the  delicate  nuclear 
membrane,  and  the  cytoplasm  packed  with  granules.  The  small  black  bodies 
clinging  to  the  periphery  of  the  egg  are  the  male  elements,  or  spermatozoa,  each 
of  which  is  also  a  single  cell. 

Draw,  showing  all  details.  The  granular  appearance  is  best  imitated  by 
stippling  with  the  point  of  the  pencil. 

B.      STUDIES    OF   TISSUES 

The  preceding  study  has  been  made  on  cells  which  are  generalized  in  structure, 
that  is  to  say,  cells  which  are  like  those  found  in  very  simple  animals  and  which 
have  not  become  specialized  for  the  performance  of  particular  functions.  In  an 
adult  organism  so  complex  as  the  frog,  however,  there  are  very  few  cells  which 
retain  this  elementary  structure,  but  most  of  them  depart  from  the  type  plan 
to  a  greater  or  less  degree,  depending  upon  the  kind  of  function  which  they  are 
called  upon  to  perform.  Moreover,  for  the  better  performance  of  these  functions, 
the  cells  become  united  into  orderly  arrangements  of  layers  or  groups,  and  these 
associations  of  cells  are  held  together  and  aided  in  the  performance  of  their  func- 
tions by  certain  materials,  which  they  themselves  secrete  and  which  are  called 
intercellular  substances.  Such  an  association  of  a  number  of  cells  of  a  particular 
kind  with  their  particular  kind  of  intercellular  substance  is  called  a  tissue.  We 
shall  now  study  the  various  kinds  of  tissues  (Holmes,  chap,  vi,  pp.  121-33). 

NOTE. — In  these  studies  of  tissues,  it  is  absolutely  essential  that  the  student 
observe  the  following  directions:  (i)  All  material  must  be  mounted  in  liquid, 
either  water  (if  dead)  or  physiological  salt  solution  (if  living).  It  is  absolutely 
useless  to  attempt  to  study  dry  material.  The  amount  of  liquid  added  should 
be  just  sufficient  to  come  to  the  edge  of  the  cover  glass.  (2)  All  material  must 
be  spread  out  as  thin  as  possible,  or  picked  into  minute  pieces  with  a  pair  of 
teasing  needles.  It  is  absolutely  useless  and  a  waste  of  time  to  try  to  study 
thick  material.  (3)  After  having  made  the  material  as  fine  as  possible,  put  a 
cover  glass  on,  lowering  it  from  one  edge  to  avoid  air  bubbles.  Excess  fluid 
should  be  absorbed.  The  cover  glass  should  not  float  around  on  the  material. 
(4)  Study  the  tissue  first  with  the  low  power  and  without  staining;  then  with  the 
high  power.  Draw  what  you  can  see  in  the  unstained  material.  (5)  Then 
stain,  if  the  directions  say  so,  and  add  what  you  can  see  after  staining  to  the 


GENERAL  HISTOLOGY:  CELLS  AND  TISSUES  27 

X 

drawing  already  made.  Use  a  small  amount  of  the  stain  and  wait  patiently 
for  it  to  take  effect.  Much  better  results  will  be  obtained  than  by  piling  on  a 
lot  of  stain  in  an  attempt  to  hurry  matters.  To  stain,  place  a  drop  of  the  stain 
in  contact  with  one  edge  of  the  cover  glass,  and  draw  it  under  by  applying  a 
piece  of  filter  paper  to  the  opposite  edge  of  the  cover  glass.  (6)  If  what  you 
see  in  your  preparation  does  not  correspond  with  the  description  in  the  outline, 
then  you  should  promptly  conclude  that  you  are  looking  at  the  wrong  thing  and 
should  seek  the  assistance  of  the  laboratory  instructor.  The  descriptions  in 
the  outline  have  been  made  as  accurate  as  possible.  (7)  Draw  only  a  few  cells, 
making  your  drawings  large  and  detailed,  putting  in  every  structure  that  you 
can  see. 

i.  Epithelial  tissues. — This  kind  of  tissue  covers  or  lines  all  the  free  surfaces 
of  the  body,  and  is  further  distinguished  by  the  relatively  unspecialized  char- 
acter of  its  cells,  which  are  similar  in  structure  and  appearance  to  the  "typical" 
cells  already  described,  and  by  the  almost  complete  absence  of  intercellular 
substance.  The  cells  are  united  into  continuous  sheets  by  a  cement  substance, 
which  is  difficult  to  demonstrate.  There  are  several  kinds  of  epithelia  (Holmes, 
pp.  121-22). 

a)  Squamous  epithelium:  Obtain  a  small  piece  of  shed  epidermis  (outer  layer 
of  the  skin)  of  the  frog,  spread  it  out  on  a  slide  in  a  drop  of  water,  cover  with  a 
cover  glass,  and  examine  with  the  low  power.     Turn  down  the  light.     Note  the 
polygonal  cells  of  which  it  is  composed,  giving  a  characteristic  mosaic  appear- 
ance; these  cells  are  found  to  be  very  thin  and  flat  when  viewed  from  the  side. 
Study  a  cell  with  the  high  power,  note  the  nucleus  and  (in  some  cases)  the  pig- 
ment granules  in  the  cytoplasm.     If  the  nucleus  is  not  clearly 'visible,  stain  with 
a  drop  of  aceto-carmine.     (See  general  directions  for  method  of  staining.)     By 
changing  the  focus  of  the  microscope  determine  whether  the  epidermis  is  one 
or  •more  layers  of  cells  thick.     Draw,  showing  a  few  of  the  cells. 

b)  Columnar  epithelium:  In  contrast  to  the  preceding,  this  type  of  epithelium 
is  characterized  by  the  tall  and  slender  shape  of  its  cells.     Obtain  a  small  piece 
of  the  inner  lining  of  the  small  intestine  which  has  been  macerated  for  twenty- 
four  hours  in  5  per  cent  chloral  hydrate,  add  a  few  drops  of  salt  solution,  tear  it 
into  the  smallest  possible  bits  with  a  pair  of  teasing  needles,  cover  and  examine 
with  the  high  power.     Look  for  slender  cells,  slightly  broader  at  one  end  and 
narrower  or  irregularly  branched  at  the  other.     The  oval  nucleus  occupies  an 
enlargement  which  is  usually  nearer  the  narrow  end.     In  some  of  the  cells  the 
broader  end  will  be  found  to  contain  a  cup-shaped  cavity  which  in  life  is  filled 
with  mucus.     Such  cells  are  called  goblet  cells.     Draw  a  few  of  the  cells.     If  the 
nucleus  is  not  visible,  stain  with  a  little  aceto-carmine.     In  their  natural  position 
these  cells  form  a  single  layer  lining  the  cavity  of  the  intestine,  their  long  axes 
parallel  to  each  other,  and  their  broad  ends  facing  the  cavity. 


28  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

c)  Ciliated  epithelium:  Have  the  assistant  give  you  a  little  tissue  scraped 
from  the  roof  of  the  mouth  of  a  freshly  pithed  frog.  Mount  the  scrapings  in 
0.6  per  cent  salt  solution,  tease  into  small  bits,  cover  and  examine.  Search  the 
field  until  a  shimmering  movement  is  seen;  then  put  on  the  high  power.  Note 
the  groups  of  cells  with  one  surface  covered  with  delicate  hairlike  processes  of  the 
cytoplasm,  called  cilia,  which  keep  up  a  rapid  vibration,  sufficiently  strong  to 
move  small  particles  in  the  vicinity  or  to  cause  the  cells  themselves  to  whirl 
around.  You  may  be  able  to  find  some  single  cells.  In  that  case  note  that  while 
the  cells  in  groups  are  more  or  less  polyhedral  in  shape,  with  flat  sides,  the  isolated 
cells  tend  to  become  spherical.  These  ciliated  epithelial  cells  are  arranged  in  a 
layer  lining  the  roof  of  the  mouth  cavity,  with  their  ciliated  surfaces  toward  the 
cavity,  and  as  the  cilia  of  all  the  cells  act  in  co-ordination,  moving  in  waves 
which  always  travel  in  the  same  direction,  a  current  is  set  up  in  that  direction, 
as  already  demonstrated  (experiment  under  II,  B,  4).  Draw. 

2.  Muscular  tissue. — The  cells  composing  muscular  tissue  are  distinguished 
physiologically  by  their  property  of  contractility,  and  morphologically  by  their 
long  and  slender  form  and  fibrillar  structure.  As  in  the  preceding  kind  of  tissue, 
there  is  relatively  little  intercellular  substance  present  (Holmes,  pp.  128-31). 

a)  Involuntary,  unstriated,  or  smooth  muscle:   Obtain  a  small  piece  of  frog 
intestine  which  has  been  macerated,  mount  it  in  salt  solution,  tease  with  needles 
into  the  smallest  possible  bits,  cover  and  examine.    Notice  that  this  material 
consists  of  very  long  and  slender,  almost  threadlike  cells,  running  parallel,  in 
layers  at  right  angles  to  each  other.     It  is  often  difficult  to  actually  isolate  a 
single  one  of  these  long  cells,  but  if  you  have  teased  your  material  carefully,  you 
will  generally  find  a  few  nearly  separate  cells  along  the  frayed  edges  of  the  general 
mass.     Each  long  fiber,  which  is  an  involuntary  muscle  cell,  possesses  an  elliptical 
nucleus,  usually  faintly  visible  in  the  unstained  material.     If  desired,  the  aceto- 
carmine  stain  may  be  applied  to  render  the  nuclei  more  distinct.     Draw.     (It 
may  be  remarked  here  for  the  benefit  of  the  student  that  the  figure  in  Holmes 
of  these  cells,  Fig.  35,  is  somewhat  inaccurate  in  respect  to  their  length.) 

b)  Voluntary  or  striated  muscle:  Cut  out  a  small  piece  from  the  leg  muscles 
of  your  preserved  frog  or  from  a  recently  pithed  frog  (the  former  is  often  bet'ter 
for  the  purpose),  mount  in  salt  solution,  tease  carefully  in  the  direction  of  the 
long  axis  of  the  muscle  until  you  have  separated  your  piece  into  threads,  cover 
and  examine.     The  long  cylindrical  objects  which  you  will  see  are  the  muscle 
cells,  or  muscle  fibers,  and  each  voluntary  muscle  is  composed  of  a  great  many 
such  fibers.     They  are  very  large  compared  to  the  other  cells  which  we  have  been 
studying,  and  in  fact  are  so  long  that  it  is  impossible' to  obtain  a  complete  one; 
hence  the  ends  are  broken.     Each  fiber  is  covered  by  a  delicate  cell  wall,  called 
in  this  case  the  sarcolemma,  and  is  crossed  by  conspicuous  alternately  light  and 
dark  transverse  bands  (really  disks,  as  the  muscle  is  cylindrical).     It  is  because 
of  these  bands,  which  probably  represent  differences  in  the  consistency  of  the 


GENERAL  PHYSIOLOGY  OF  THE  FROG  29 

muscle  substance,  that  voluntary  muscle  is  called  "striped"  muscle.  A  longi- 
tudinal striation  may  also  usually  be  seen,  indicating  that  the  muscle  fiber  is 
really  composed  of  a  number  of  much  smaller  longitudinal  fibers,  known  as 
fibrillae  or  sarcostyles,  which  are  bound  together  in  the  same  sarcolemma.  Each 
muscle  fiber  contains  a  number  of  slender  nuclei,  located  near  the  surface,  just 
under  the  sarcolemma.  In  order  to  see  them  it  will  generally  be  necessary  to 
apply  the  aceto-carmine  stain.  Since  the  young  muscle  cell  possesses  but  a 
single  nucleus,  and  since  the  others  are  produced  by  the  division  of  this  nucleus, 
it  is  probable  that  the  adult  muscle  fiber  is  not  a  single  cell  but  a  number  of  cells 
with  no  cell  walls  between.  Such  a  multinucleate  structure  is  called  a  syncytium. 
Draw  a  muscle  cell  showing  all  structures. 

3.  Connective  tissue. — In  this  type  of  tissue,  the  cells  are  much  reduced 
and  few  in  number,  and  the  greater  bulk  of  the  tissue  consists  of  intercellular 
substance.  The  function  of  the  connective  tissue  is  that  of  supporting  and 
binding  other  parts  and  tissues.  It  is  therefore  exceedingly  widespread  (Holmes, 
pp.  123-28). 

a)  White  fibrous  or  collagenous  connective  tissue:   This  is  the  white  weblike 
material  binding  the  muscles  of  the  frog  together  or  forming  the  partitions 
between  the  subcutaneous  lymph  sacs.     Remove  some  from  either  of  these  places 
of  your  preserved  frog,  spread  it  out  carefully  on  a  slide  so  as  to  make  a  very 
thin  layer,  add  salt  solution,  cover  and  examine.     It  consists  for  the  most  part 
of  long,  slender,  wavy  fibers,  running  in  all  directions.     These  are  the  white  or 
collagenous  fibers  (so  called  because  when  boiled  they  form  glue) ;  they  are  very 
tough  and  inelastic.    Another  type  of  fiber,  the  yellow  elastic  fibers,  is  present 
in  small  numbers,  distinguishable  by  the  fact  that  they  run  straight  and  singly, 
not  in  bundles  as  do  the  white  ones.     The  fibers  of  connective  tissue  are  not 
cells,  and  are  probably  not  living,  but  they  are  the  intercellular  products  of  the 
real  connective  tissue  cells.     In  order  to  see  these  latter,  apply  the  aceto-carmine 
stain,  and  note  after  a  few  minutes  the  oval  nuclei  of  the  connective  tissue  cells 
staining  deep  pink  or  red,  scattered  among  the  fibers.    The  acetic  acid  in  the 
stain  will  also  tend  to  dissolve  the  white  fibers,  making  the  yellow  elastic  ones 
more  distinct.     Cells  and  fibers  are  imbedded  in  an  invisible,  clear,  gelatinous 
matrix  which  is  also  secreted  by  the  cells.     Draw  a  small  portion  of  the  tissue, 
showing  fibers  and  nuclei. 

b)  Cartilage:  Have  the  assistant  slice  off  with  a  razor  a  thin  piece  of  cartilage 
from  the  end  of  the  one  of  the  long  limb  bones  of  a  recently  pithed  frog,  mount 
in  salt  solution,  cover  and  examine.    The  prepared  slide  "Frog — cartilage"  may 
also  be  used.     Cartilage  consists  of  a  clear  matrix  which  is  much  more  dense  and 
firm  than  in  the  previous  type  of 'connective  tissue.     In  this  matrix  are  rounded 
spaces  or  lacunae,  at  intervals,  which  are  completely  filled  in  the  living  material 
by  the  cartilage  cells,  which  secrete  the  matrix.    When  two  or  more  cells  are 
contained  in  one  lacuna,  they  have  originated  through  the  division  of  a  previous 


30  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

single  cell,  and  will  become  separated  from  each  other  by  the  deposit  of  matrix 
between  them.     Draw  a  small  portion  of  cartilage. 

c)  Bone:  Examine  prepared  slide  "Frog — bone."  These  slides  are  prepared 
by  grinding  down  slices  of  dried  bone;  hence  the  bone  cells  and  other  living 
structures  of  the  bone  have  been  destroyed.  In  bone,  the  matrix  has  been 
rendered  very  firm  and  strong  by  the  deposit  in  it  of  mineral  salts,  chiefly  cal- 
cium phosphate  and  calcium  carbonate,  through  the  activity  of  the  bone  cells. 
This  matrix  is  arranged  in  concentric  layers,  called  lamellae,  around  circular 
holes,  which  are  the  cross-sections  of  canals,  the  Eaversian  canals.  The  Haver- 
sian  canals  traverse  the  bone  in  a  longitudinal  direction  and  in  life  carry  blood 
vessels,  lymph  vessels,  and  nerves  for  the  nutrition  of  the  bone.  Scattered 
through  the  lamellae  are  minute  spaces,  or  lacunae,  with  spidery  processes  extend- 
ing out  into  the  matrix.  In  these  spaces  the  bone  cells  and  their  processes  are 
contained  in  the  living  condition.  Draw  a  portion  of  bone. 

4.  Blood. — Blood  may  be  regarded  as  tissue  in  which  the  intercellular  sub 
stance  is  liquid.     The  cells  of  blood  are  called  corpuscles,  and  the  fluid  inter- 
cellular portion,  the  plasma.    The  corpuscles  are  of  two  general  classes,  red 
corpuscles,  which  give  the  red  color  to  the  blood  and  carry  oxygen,  and  white 
corpuscles,  which  protect  the  body  from  disease  (Holmes,  pp.  258-64). 

a)  Fresh  blood:  Obtain  from  the  assistant  a  drop  of  fresh  frog  blood,  stir  it 
up  in  salt  solution,  cover  and  examine  with  the  high  power.    The  numerous 
oval  bodies  are  the  red  blood  corpuscles,  although  they  are  not  red  except  in 
masses.     Scattered  here  and  there  among  the  red  corpuscles  will  be  found  the 
white  corpuscles,  smaller,  irregular  in  shape,  and  with  granular  cytoplasm.     If 
you  watch  a  white  corpuscle  for  some  time  you  may  see  it  undergo  slow  changes 
of  shape,  an  example  of  amoeboid  movement.    By  gently  moving  the  cover  glass, 
cause  the  red  corpuscles  to  float  about  on  the  slide,  and  as  they  turn  determine 
their  shape  in  profile.    The  central  bulge  is  due  to  the  nucleus,  which  is  generally 
faintly  visible. 

b)  Stained  blood:  Examine  with  the  high  power  the  slide  of  blood.    Note: 

(1)  The  red  blood  corpuscles,  the  very  numerous  oval  bodies,  on  the  slide. 
Each  has  a  central  nucleus.     Draw  one. 

(2)  The  white  blood  corpuscles:    As  these  are  much  less  numerous  than  the 
red  corpuscles,  it  will  be  necessary  to  search  the  slide  carefully  for  them.     There 
are  several  kinds  of  white  corpuscles.    Those  with  a  complex  nucleus,  consisting 
of  several  pieces,  and  with  granular  cytoplasm  are  called  leucocytes;  those  with 
an  ordinary  type  of  nucleus  and  with  clear  cytoplasm  are  lymphocytes.    Try  to 
identify  the  following  kinds  and  make  drawings  of  those  which  you  are  able  to 
find: 

(a)  Polymorphonuclear  leucocytes:  This  type  of  white  blood  cell  is  distin- 
guished by  its  very  irregular  nucleus,  which  consists  of  several  masses,  apparently 
separate  but  really  united  by  delicate  strands.  The  cytoplasm  is  always  packed 


GENERAL  HISTOLOGY:  CELLS  AND  TISSUES  31 

with  granules,  which  are  fine  in  the  common  type  of  leucocyte,  coarse  in  a  rarer 
type. 

(b)  Large  lymphocytes:  These  are  nearly  spherical  cells,  with  clear  cytoplasm 
and  a  small  rounded  nucleus. 

(c)  Small  lymphocytes:  They  are  smaller  than  the  preceding  with  relatively 
large  nuclei,  covered  by  a  small  rim  of  cytoplasm. 

5.  Nervous  tissue. — Nervous  tissue  is  composed  of  nerve  cells,  and  the  struc- 
tures which  support  them  (Holmes,  pp.  131-33).  A  nerve  cell  consists  of  a 
central  portion,  called  the  cell  body  which  contains  a  large  nucleus,  and  of  slender 
processes  which  extend  out  from  this  cell  body  often  to  long  distances.  Portions 
of  nervous  tissue  which  consist  almost  entirely  of  cell  bodies  are  designated  as 
gray  matter,  while  those  which  consist  of  the  processes  constitute  the  white  matter. 
The  processes  of  a  nerve  cell  are  of  two  kinds:  those  that  convey  the  impulses  into 
the  cell,  called  dendrites,  usually  very  numerous  and  much  branched,  and  that 
one  which  conveys  the  impulse  away  from  the  cell,  always  single  and  unbranched 
or  slightly  branched,  named  the  axone.  What  are  called  nerves  are  bundles  of 
axones. 

a)  Brain  cells:  In  order  to  demonstrate  the  entire  nerve  cell  with  its  processes 
it  is  necessary  to  cut  thick  slices  of  the  brain,  and  to  devise  a  special  staining 
method  since  the  processes  do  not  take  ordinary  stains.    A  method  was  originated 
by  an  Italian  histologist  named  Golgi,  by  which  the  entire  cell  is  blackened  by  a 
deposit  of  silver  upon  it.     Examine  a  slide  of  brain  provided,  stained  by  the 
Golgi  method,  either  brain  cells  of  the  rabbit  (Lepus),  or  human  cerebellum. 
Use  low  power  only,  as  the  sections  are  thick.    Note  the  numerous  black  branched 
objects  upon  the  slide.     Each  is  a  nerve  cell  with  its  processes.    Pick  out  a 
favorable  place  on  the  slide  (4)  and  study  one  of  the  cells.     Each  consists  of  a 
rounded  or  triangular  cell  body  from  which  spring  several  processes.     In  the 
case  of  the  rabbit,  one  large,  stout  process  springs  from  the  pointed  end  of  the 
cell  body  and  several  branched  processes  from  the  rounded  end.     In  the  cells 
of  the  cerebellum,  two  or  three  stout  processes  (dendrites)  spring  from  one  side 
of  the  cell  and  immediately  break  up  into  an  exceedingly  complicated  system 
of  branches,  while  from  the  opposite  surface  of  the  cell  the  small  slender  axone 
arises  (it  is  not  always  visible).     Draw  a  brain  cell. 

b)  Motor  cells  of  the  spinal  cord  of  the  frog:    In  order  to  demonstrate  the 
actual  structure  of  the  cell  body,  the  usual  thin  sections,  stained  in  the  ordinary 
way,  are  employed.     Examine  the  slide  "Spinal  cord — frog"  with  your  lowest 
power.     Identify  the  central  large  oval  body  on  the  slide  (all  other  objects  are 
to  be  disregarded).     In  this  oval  object,  which  is  the  cross-section  of  the  spinal 
cord,  observe  two  general  regions,  a  central,  denser,  slightly  darker  region,  the 
gray  matter,  trapezoidal  in  shape  and  containing  numerous  darkly  stained  cell 
bodies;    and  an  outer  region,  lighter,  more  open,  and  with  only  a  few  small 
cell  bodies,  the  white  matter.     In  the  two  corners  of  the  lower  base  of  the  trapezoid 


32  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

formed  by  the  gray  matter  locate  several  very  large  cells.  These  are  the  motor 
cells  whose  axones  extend  out  to  the  voluntary  muscles  of  the  body.  Examine 
one  of  these  with  the  high  power.  The  structure  of  the  cell  body  is  well  shown, 
but  only  the  beginnings  of  the  processes  are  present.  (Why?)  Study  the 
structure  of  the  cell  body,  comparing  with  other  cells  already  seen.  Note  the 
relatively  large  nucleus,  containing  a  conspicuous  round  body,  the  nudeolus, 
but  very  few  chromatin  granules,  and  the  granular,  sometimes  nbrillar  structure 
of  the  cytoplasm.  Draw. 

c)  Structure  of  a  nerve:  Obtain  a  small  piece  of  fresh  nerve  from  a  recently 
pithed  frog.  Mount  in  salt  solution  and  tease  with  needles  in  a  longitudinal 
direction  until  you  have  separated  it  out  into  minute  fibers.  Cover  and  examine. 
The  nerve  is  seen  to  be  made  up  of  a  number  of  cylindrical  fibers,  bound  together 
by  connective  tissue.  Each  of  the  fibers  is  in  fact  a  single  axone  of  a  nerve  cell. 
Find  an  isolated  fiber  and  examine  with  the  high  power.  It  consists  of  a  central 
transparent  region,  the  axone  itself,  often  called  here  the  axis  cylinder,  and  a 
thick  sheath  surrounding  this,  which  is  known  as  the  medullary  sheath.  The 
The  sheath  is  composed  of  a  fatty  substance,  called  myelin,  which  tends  to  swell 
up  and  become  distorted  in  the  preparation.  Outside  of  the  medullary  sheath 
is  a  delicate  cell  wall,  the  neurilemma.  Draw. 

6.  Reproductive  cells. — 

a)  Eggs:   The  eggs  or  ova  of  animals  are  the  largest  cells,  although  their 
great  size  is  generally  due  to  the  large  amount  of  inert  food  material  (yolk) 
which  they  contain.    The  eggs  of  the  frog  are  the  spherical  black  and  white 
protuberances  which  have  already  been  noted  on  the  surface  of  the  ovaries. 

b)  Spermatozoa:  The  spermatozoa  of  the  frog  are  best  studied  in  the  spring, 
when  the  animals  are  sexually  active,  as  at  other  seasons  they  are  apt  to  be 
non-motile  and  imperfectly  developed.     In  such  case,  spermatozoa  of  a  guinea- 
pig  or  rat  should  be  examined  instead.     Take  a  small  portion  of  the  testis  of  a 
freshly  killed  frog  or  other  animal,  tease  in  salt  solution,  cover  and  examine 
(Holmes,  p.  216).    The  preparation  will  contain  thousands  of  minute,  slender, 
rapidly  moving  objects,  the  spermatozoa.     They  are  peculiarly  modified  cells. 
In  the  frog  each  possesses  a  rodlike,  slightly  curved,  head,  which  is  practically 
nothing  but  the  nucleus,  and  a  long,  very  slender,  vibratile  tail,  which  represents 
the  cytoplasm.     The  spermatozoa  of  other  animals  generally   have   smaller 
rounded  heads  and  longer  tails  than  those  of  the  frog.     Draw  a  spermatozoon. 


IV.     GENERAL  HISTOLOGY:    STRUCTURE  OF  ORGANS 

An  organ  consists  of  two  or  more  kinds  of  tissue  united  together  in  a  definite 
and  characteristic  way  for  the  performance  of  specific  functions. 

A.      STRUCTURE   OF  THE   LIVER 

Examine  slide  "  Necturus — liver"  (see  Holmes,  pp.  153-56).  The  liver  may 
be  taken  as  an  example  of  a  rather  simply  constructed  organ,  and  also  as  an 
example  of  a  secreting  gland.  It  consists  almost  entirely  of  large  cuboidal 
epithelial  cells,  arranged  in  cylindrical  columns  which  branch  and  connect  with 
each  other  in  a  very  irregular  manner.  The  columns  therefore  form  a  kind  of 
network  with  numerous  large  spaces  between  them.  These  spaces  are  capil- 
laries and  in  them  blood  corpuscles  will  usually  be  found.  A  very  slender, 
usually  invisible  canal  runs  down  the  center  of  each  liver  column  between  the 
cells,  and  into  this  canal,  which  is  called  a  bile  capillary,  the  secretion  of  the  liver 
cells,  known  as  bile,  is  poured.  The  large  black  spots  scattered  abundantly 
through  the  liver  are  collections  of  pigment  granules.  Large  blood  vessels,  and 
perhaps  some  of  the  bile  ducts  which  collect  the  bile  from  the  bile  capillaries,  may 
be  present  on  the  section.  Surrounding  the  liver  and  penetrating  it  here  and 
there  along  the  course  of  the  larger  blood  vessels  is  a  small  amount  of  white 
fibrous  connective  tissue.  The  liver  cells  have  several  other  highly  important 
functions  besides  that  of  secreting  bile. 

B.      STRUCTURE   OF  THE  INTESTINE 

Examine  slide  "  Necturus— intestine"  (see  Holmes,  pp.  148-50).  These 
cross-sections  of  the  small  intestine  have  been  stained  with  Mallory's  connective 
tissue  stain  in  order  to  produce  a  marked  color  contrast  between  the  different 
layers  of  the  intestinal  wall.  This  stain  dyes  connective  tissue  and  related  sub- 
stances a  deep  blue  color,  and  nuclei  orange  or  red. 

i.  General  structure  of  the  intestinal  wall.— The  wall  of  the  intestine  con- 
sists of  four  coats.  Identify  these  as  follows  with  the  low  power,  beginning  next 
to  the  cavity: 

a)  The  mucous  coat  (mucous  membrane  or  tunica  mucosa],  the  innermost 
light-colored  layer,  containing  numerous  red  or  orange  nuclei.     It  is  thrown  up 
into  folds  and  is  sharply  separated  from  the  next  layer  by  its  different  reaction 
to  the  dye. 

b)  The  submucous  coat  (tela  submucosd),  a  broad  band,  stained  deep  blue, 
containing  frequent  spaces  and  extending  up  into  the  folds  of  the  mucosa. 

33 


34  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

c)  The  muscular  coat  (tunica  muscularis),  the  remainder  of  the  intestinal 
wall,  consisting  of  two  strata: 

(1)  The  circular  muscle  layer  (stratum  circulare)  the  inner  layer,  in  which  the 
muscles  run  in  a  circular  direction. 

(2)  The  longitudinal  muscle  layer  (stratum  longitudinale) ,  the  outer  layer, 
in  which  the  muscles  run  in  a  longitudinal  direction.     This  layer  also  contains 
a  considerable  quantity  of  connective  tissue  and  hence  takes  more  of  the  blue 
stain  than  the  preceding  layer. 

d)  The  serous  coat  (tunica  serosa,  or  visceral  peritoneum),  a  very  thin  mem- 
brane covering  the  outside  of  the  intestine,  invisible  under  the  low  power.     It  is 
not  really  a  part  of  the  intestinal  wall  but  the  peritoneum  investing  the  intestine. 

2.  Detailed  structure  of  the  intestinal  wall. — Select  a  favorable  place  where 
the  mucous  membrane  is  cut  parallel  to  the  long  axes  of  its  cells.  The  best 
places  are  generally  at  the  bottom  of  the  folds.  Study  with  the  high  power. 

a)  The  mucous  membrane  consists  of  the  lining  epithelium  of  the  intestine 
and  subjacent  parts.    This  lining  epithelium  is  composed  of  a  single  layer  of 
tall  columnar  cells,  each  extending  from  the  cavity  of  the  intestine  to  the  under- 
lying connective  tissue  (stained  blue).    These  cells  were  studied  in  Section  III, 
B,  i,  b.    The  cell  walls  are  frequently  difficult  to  see.     Each  cell  possesses 
near  its  base  a  large  oval  granular  nucleus,  stained  red  or  orange.     Why  do  the 
nuclei  appear  so  numerous  (-4)?    Are  they  all  in  the  same  plane  (determine  this 
by  changing  the  focus)?    The  free  ends  (ends  next  the  cavity)  of  many  of  the 
epithelial  cells  contain  flask-shaped  depressions,  called  goblets,  which  are  filled 
with  mucus.    As  mucus  is  chemically  related  to  connective  tissue,  the  goblets 
are  dyed  blue  by  Mallory's  stain.     There  are   thus   two  kinds   of   cells   in 
the  epithelium,  the  ordinary  columnar  cells  and  the  goblet  cells.    Understand  the 
different  appearance   of  various   parts   of   the  mucosa  by   considering  that 
the  plane  of  the  section  may  not  necessarily  be  parallel  to  the  long  axes  of 
the  epithelial  cells. 

The  tissue  immediately  in  contact  with  the  epithelium  and  accompanying 
it  in  all  its  foldings  is  considered  to  be  a  part  of  the  mucous  membrane.  It  is 
designated  as  the  tunica  propria  or  stroma,  and  consists  of  loosely  woven  white 
connective  tissue  fibrils,  which  run  in  general  parallel  to  the  epithelium.  The 
connective  tissue  cells  (of  which  only  the  nuclei  are  distinctly  visible)  are  more 
numerous  here  than  in  the  next  layer.  However,  no  sharp  distinction  can  be 
drawn  between  the  tunica  propria  and  the  submucous  coat.  The  tunica  propria 
is  abundantly  perforated  by  blood  and  lymph  spaces,  and  contains  little  nests 
of  cells  whose  function  is  not  clear. 

b)  The  submucous  coat  is  composed  of  white  fibrous  connective  tissue  con- 
tinuous with  the  tunica  propria,  but  its  fibers  do  not  run  parallel  to  the  cavity 
of  the  intestine.     Note  in  it  the  scattered  connective  tissue  cells  and  the  many 
large  lymph  and  blood  vessels. 


GENERAL  HISTOLOGY:   STRUCTURE  OF  ORGANS  35 

c)  The  circular  muscle  layer  consists  of  smooth  muscle  cells  running  parallel 
to  the  plane  of  section.     The  boundaries  of  the  individual  muscle  cells  are  not 
clear,  but  the  whole  layer  appears  to  be  made  up  of  parallel  fibrillar  stria tions. 
The  conspicuous  nuclei  are  long  and  spindle-shaped. 

d)  The  longitudinal  muscle  layer  contains  a  considerable  quantity  of  white 
fibrous  connective  tissue  which  stains  blue,  in  which  are  imbedded  smooth 
muscle  cells  running  at  right  angles  to  the  plane  of  section,  and  thus  appearing 
as  circles.     Understand  why  the  nuclei  may  or  may  not  appear  in  the  circular 
cross-section.     Numerous  blood  vessels  are  present  in  this  layer. 

e)  The  serous  coat  is  a  very  thin  membrane  looking  like  a  line  closely  applied 
to  the  outer  surface  of  the  preceding  coat.    At  intervals  its  flattened  nuclei  are 
seen.     As  already  explained  the  serous  coat  is  the  visceral  peritoneum. 

Draw  a  small  portion  of  the  intestinal  wall  showing  the  appearance  and  cell 
structure  of  the  fiber  layers  accurately  and  in  detail.  The  drawing  should  be 
four  or  five  inches  in  width. 

C.      STRUCTURE   OF  THE   STOMACH 

Examine  slide  "Frog — stomach"  (see  Holmes,  p.  140).  Observe  that  the 
general  appearance  and  arrangement  of  layers  of  the  stomach  wall  are  the  same 
as  in  the  case  of  the  small  intestine,  except  that  the  coats  are  thicker,  especially 
the  mucous  and  muscular  coats.  Tlie  particular  point  of  interest  about  the 
stomach  wall  is  the  formation  of  glands  in  the  mucosa. 

i.  The  gastric  glands. — The  mucosa  of  the  stomach  is  thrown  up  into  regu- 
lar folds  or  rugae,  which  appear  as  conical  elevations  in  section.  The  lining 
epithelium  does  not  form  an  even  layer  over  these  folds  but  is  itself  folded  in  and 
out  in  such  a  way  as  to  produce  a  large  number  of  long  tubular  glands  set  closely 
together  with  their  long  axes  parallel.  It  may  be  noted  in  passing  that  all 
glands  are  produced  by  such  infoldings  of  epithelia.  Narrow  strands  of  the 
tunica  propria  separate  the  glands  from  each  other.  Find  a  place  on  the  slide 
where  the  glands  are  cut  parallel  to  their  long  axes  and  examine  one  of  the  gastric 
glands  in  detail  with  the  high  power.  (Their  appearance  is  somewhat  different 
in  different  regions  of  the  stomach.  Consult  Holmes,  p.  140.)  The  parts  of 
a  gastric  gland  are  mouth,  neck,  and  body  or  fundus.  The  mouth  is  the  longest 
part  and  contains  a  narrow  canal  leading  from  the  interior  of  the  gland  into  the 
cavity  of  the  stomach.  The  cells  near  the  beginning  of  the  mouth  are  very  elon- 
gated, with  clear  free  ends,  probably  containing  mucus,  and  slender- tailed  nuclei. 
Farther  down  the  mouth,  the  cells  and  nuclei  become  more  rounded.  The  region 
where  the  mouth  ceases  is  the  neck  and  consists  of  a  few  cells  which  contain 
large  clear  spaces.  The  gland  may  branch  in  the  neck  region  so  that  two  or 
more  bodies  are  attached  to  one  mouth.  Below  the  neck  the  body  or  fundus  is 
composed  of  polygonal  granular  cells,  whose  function  is  to  secrete  the  gastric  juice. 

Draw  a  gastric  gland  in  detail. 


36  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

2.  The  muscularis  mucosae. — Another  difference  between  the  stomach  and 
the  intestine  is  that  the  tunica  propria  of  the  mucous  membrane  is  sharply 
bounded  from  the  submucous  coat  by  a  narrow  band  of  smooth  muscle  fibers 
which  is  called  the  muscularis  mucosae.  It  is  composed  of  the  usual  two  layers, 
an  inner  circular  and  an  outer  longitudinal  one. 


D.      STRUCTURE   OF   THE   SKIN 

Examine  slide  "Frog — skin"  (see  Holmes,  chap,  ix,  pp.  179-86).  The  skin 
is  a  combination  of  epithelial  and  connective  tissue.  The  epithelial  part  is 
called  the  epidermis;  the  connective  tissue  part,  the  dermis  or  corium. 

1.  The  epidermis. — The  epidermis  is  a  stratified  epithelium,  i.e.,  an  epi- 
thelium composed  of  several  layers  of  cells.     The  outermost  layer  of  the  epidermis 
(stratum  corneum)  consists  of  very  flat,  thin,  polygonal  cells,  which  are  cornified 
or  horny  in  composition.     These  cells  are  the  ones  which  are  shed  by  the  frog, 
and  they  have  already  been  examined  separately.     Beneath  the  stratum  corneum, 
the  cells  gradually  change  from  a  flattened  to  a  rounded,  and  finally  to  a  columnar 
shape,  until  the  innermost  ones  are  quite  columnar  in  form.    These  layers  of 
cells  constitute  the  stratum  germinativum  (also  called  stratum  mucosum,  and 
stratum  Malpighii).     The  cells  of  the  stratum  germinativum  frequently  contain 
brown  pigment  granules,  and  dark  brown  or  black  branched  pigment  cells  (chro- 
matophores)  may  be  scattered  among  the  regular  epithelial  cells. 

2.  The  dermis. — The  dermis  is  composed  of  connective  tissue,  separable  into 
two  layers,  an  outer  loose  layer,  the  stratum  spongiosum,  and  an  inner  compact 
layer,  the  stratum  compactum. 

a)  The  stratum  spongiosum:   This  consists  of  a  loose,  irregular  network  of 
connective  tissue  fibers,  inclosing  lymph  spaces,  blood  vessels,  etc.     It  contains 
a  thin  layer  of  chromatophores,  dark-colored,  irregular,  branching  cells  just 
under  the  epidermis,  and  beneath  this  the  cutaneous  glands. 

b)  The  cutaneous  glands:   These  are  produced  by  a  simple  infolding  of  the 
stratum  germinativum  of  the  epidermis,  and  their  walls  are  a  single  layer  thick. 
Each  opens  to  the  surface  of  the  skin  by  a  narrow  neck  which  passes  up  through 
the  epidermis.     Explain  why  most  of  the  glands  on  the  slide  appear  to  have  no 
neck  (A).    Also  explain  why  some  of  them  appear  to  be  solid  instead  of  hollow. 
Two  general  varieties  of  cutaneous  glands  are  recognized  in  the  frog,  the  mucus 
and  the  poison  glands. 

The  mucus  glands  are  smaller  and  much  more  numerous  than  the  poison 
glands.  Their  appearance  differs  according  to  the  stage  of  activity  in  which 
they  happen  to  be.  In  the  resting  or  inactive  state,  the  epithelial  cells  are  very 
high  and  conical  so  that  the  cavity  of  the  gland  is  practically  obliterated;  the 
nuclei  are  small  and  situated  at  the  bases  of  the  cells.  In  the  active  state,  the 
inner  ends  of  the  cells  are  converted  into  mucus  which  forms  transparent  masses 


GENERAL  HISTOLOGY:  STRUCTURE  OF  ORGANS  37 

in  the  cavity  of  the  gland,  which  now  appears  larger  than  in  the  resting  condition; 
the  cells  in  the  inactive  condition  are  smaller,  cuboidal,  with  centrally  situated 
nuclei.  Intermediate  states,  of  course,  occur  between  these  two  extremes. 

The  poison  glands  are  much  larger  than  the  mucus  glands  and  of  infrequent 
occurrence  except  on  certain  parts  of  the  skin.  There  may  be  none  on  your 
slide.  The  epithelial  cells  form  a  very  thin  layer  surrounding  the  very  large 
cavity,  and  frequently  the  cell  walls  are  not  distinct.  The  secretion,  which  is 
poisonous,  appears  as  granular  masses  near  the  epithelium. 

Each  of  the  glands  is  invested  with  a  thin  layer  of  smooth  muscles,  and  outside 
of  this  a  layer  of  connective  tissue.  Neither  of  these  layers  can  be  clearly  made 
out  in  the  preparations. 

c)  The  stratum  compactum:  This  consists  of  a  dense  layer  of  white  connective 
tissue  fibers,  arranged  parallel  to  the  surface  of  the  skin.     At  intervals,  vertical 
strands,  consisting  of  connective  tissue,  smooth  muscle  cells,  blood  vessels, 
nerves,  etc.,  cross  the  wavy  layers  of  the  stratum  compactum  at  right  angles, 
and  may  extend  up  into  the  epidermis. 

d)  The  subcutaneous  connective  tissue:    Beneath  the  stratum  compactum 
occurs  loose  connective  tissue  which  is  not  a  part  of  the  skin  but  forms  the 
boundaries  of  the  subcutaneous  lymph  sacs. 

Draw  a  portion  of  the  skin,  showing  in  detail  the  structure  of  all  the  layers. 

E.      STRUCTURE   OF  THE   KIDNEY 

Examine  slide  "Frog — kidney"  (see  Holmes,  pp.  202-6).  The  section  is 
taken  across  the  kidney.  The  flattened  surface  is  ventral;  the  rounded  surface 
dorsal.  In  the  middle  of  the  ventral  surface,  observe  a  yellowish  or  orange  mass, 
the  adrenal  gland,  made  up  of  masses  of  epithelial  cells  (this  is  not  present  on  all 
sections) ;  and  in  this  region  also  there  are  usually  seen  sections  of  large  arteries 
and  veins.  The  two  sides  of  the  kidney  may  be  distinguished  in  section  as 
follows:  the  outer  edge  is  more  pointed  and  contains  cross-sections  of  a  large 
vein,  the  renal  portal  vein,  and  the  ureter. 

1.  The  tubules. — The  greater  portion  of  the  kidney  is  made  up  of  extremely 
long  tubular  glands,  called  tubules,  which  are  much  coiled  and  twisted.     Because 
of  this  coiling,  the  tubules  appear  in  section  as  circles,  ellipses,  crescents,  etc. 
Each  tubule  possesses  a  large  and  distinct  central  cavity,  and  its  wall  consists 
of  a  single  layer  of  cuboidal  epithelial  cells,  whose  function  is  to  extract  the 
nitrogenous  waste  matters  from  the  blood.    Note  the  numerous  blood  vessels 
between  the  tubules,  and  the  connective  tissue  between  the  tubules  and  covering 
the  surface  of  the  kidney. 

2.  The  Malpighian  bodies  or  renal  corpuscles. — Each  uriniferous  tubule 
begins  in  a  Malpighian  body,  little  rounded  masses  situated  near  the  ventral 
surface.     Examine  one  of  these  with  the  high  power.     It  consists  of  a  dense  tuft 


38  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

of  capillaries,  called  a  glomerulus,  around  which  the  beginning  of  the  tubule 
forms  a  very  thin  cup-shaped  inclosing  membrane,  the  Bowman's  capsule. 
Through  the  opening  of  the  cup  an  artery  enters  the  glomerulus,  and  a  vein 
leaves  it;  opposite  this  point  the  uriniferous  tubule  begins.  You  will  probably 
have  to  examine  a  number  of  Malpighian  bodies  in  order  to  see  all  of  these  points. 
The  tubule  after  leaving  the  Malpighian  body  winds  in  a  complicated  way 
through  the  substance  of  the  kidney  and  finally  empties  into  a  collecting  tubule 
which  opens  into  the  ureter. 

F.      STRUCTURE   OF   THE   SPINAL   CORD 

Examine  slide  "Frog — spinal  cord"  (see  Holmes,  p.  286).  The  spinal  cord, 
as  we  have  seen,  consists  of  the  central  gray  matter,  composed  of  nerve-cell 
bodies,  and  the  peripheral  white  matter,  composed  of  nerve-cell  processes.  In 
the  center  of  the  gray  matter  is  a  small  canal,  the  central  canal.  The  four  corners 
of  the  gray  matter  are  produced  into  processes,  known  as  the  dorsal  and  ventral 
horns,  or  cornua  of  the  gray  matter.  The  ventral  horns  are  considerably  broader 
than  the  dorsal  horns,  and  contain  the  large  motor  cells  which  have  already 
been  examined.  The  spinal  cord  is  nearly  separated  into  two  symmetrical 
halves  by  the  dorsal  and  ventral  fissures,  which  extend  from  the  middle  of  the 
dorsal  and  ventral  sides  in  toward  the  central  canal.  The  dorsal  fissure  is  shallow 
and  is  continued  toward  the  central  canal  by  a  narrow  septum,  composed  of 
loose  tissue.  The  ventral  fissure  is  much  deeper  and  extends  nearly  to  the 
central  canal;  it  incloses  an  artery,  the  ventral  spinal  artery. 

The  white  matter  consists  mostly  of  cross-sections  of  the  nerve  fibers,  which 
take  their  origin  from  the  cells  of  the  gray  matter.  In  addition  to  the  nerve 
fibers,  the  white  matter  contains  scattered  cells,  which  are  mainly  the  cells  of 
the  neuroglia,  a  peculiar  kind  of  connective  tissue,  found  only  in  the  nervous 
system.  The  neuroglia  forms  a  network  supporting  the  nervous  structures. 

The  cord  is  surrounded  by  a  sheath,  the  pia  mater,  composed  of  connective 
tissue,  and  containing  numerous  blood  vessels. 

Draw  the  section  of  the  cord,  showing  the  above-mentioned  features. 

The  instructor  will  be  glad  to  lend  sections  of  other  organs  of  the  frog  to 
students  who  care  to  see  them. 


V.     THE  SPECIAL  ANATOMY  OF  THE  FROG 

We  have  seen  that  organisms  are  composed  of  cells,  that  cells  are  combined 
to  form  tissues,  and  tissues  to  make  up  organs.  The  organs  are  united  in  groups 
called  systems.  We  have  already  studied  these  systems  in  a  general  way,  and 
they  are  now  to  be  studied  in  detail. 

A.      THE  DIGESTIVE   SYSTEM 

1.  Esophagus. — Use  your  preserved  frog.     Cut  through  the  tissues  bound- 
ing the  anterior  wall  of  the  coelome  to  the  left  of  the  left  lung,  and  turn  the  lung 
and  heart  to  the  right.     This  exposes  the  esophagus.    It  extends  from  the  end 
of  the  mouth  cavity,  called  the  pharynx,  to  the  stomach.    A  slight  enlargement 
usually  marks  the  beginning  of  the  stomach  (Holmes,  pp.  138-42). 

2.  Stomach — The  end  of  the  stomach  continuous  with  the  esophagus  is 
called  the  cardiac  end;  the  opposite  end  is  the  pyloric  end,  and  is  marked  by  a 
constriction,  the  pylorus.     Slit  open  the  stomach  by  a  longitudinal  slit  from 
cardiac  to  pyloric  end.     Note  the  longitudinal  ridges,  or  rugae,  in  the  lining  of 
the  stomach,  and  compare  with  the  lining  of  the  esophagus  and  small  intestine. 
Examine  the  cut  surface,  and  note  that  the  layers  of  the  stomach  wall,  which 
have  already  been  seen  in  microscopic  section,  can  be  distinguished  with  the 
naked  eye.     The  mucosa  and  submucosa  appear  as  a  single  layer,  which  can  be 
separated  from  the  underlying  thick  circular  muscle  layer;    the  longitudinal 
muscle  layer  forms  a  thin  white  outer  coat. 

3.  The  small  intestine. — The  first  part  of  the  small  intestine  is  called 
duodenum,  and  it  receives  the  common  bile  duct  which  carries  the  secretions  of  the 
liver  and  pancreas.     The  remaining  coiled  part  of  the  small  intestine  is  the 
ileum  (Holmes,  p.  148). 

4.  The  liver. — The  liver  consists  of  the  following  parts:  The  left  lobe  is  the 
largest,  and  is  divided  by  a  deep  fissure  into  an  anterior  part,  which  lies  to  the 
left,  and  a  posterior  part  which  occupies  the  middle.    The  right  lobe  is  not  sub- 
divided, but  lies  to  the  right  of  the  median  line  extending  somewhat  dorsally. 
The  middle  lobe  of  the  liver  is  not  visible  ventrally  unless  the  other  lobes  are 
pushed  apart.     It  then  appears  as  a  small  squarish  lobe  extending  far  dorsally 
and  continuous  with  the  posterior  part  of  the  left  lobe.    Between  the  right  lobe 
and  the  posterior  part  of  the  left  lobe  on  the  dorsal  side  is  the  green  round  gall 
bladder  (Holmes,  p.  152). 

5.  The  pancreas. — Turn  the  lobes  of  the  liver  forward  and  study  the  pancreas. 
It  is  an  irregular,  branched,  yellowish  gland  lying  in  the  gastro-hepato-duodenal 

39 


40  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

ligament.  It  sends  down  two  tail-like  processes  to  the  duodenum,  and  another 
process,  the  hepatic  process,  along  the  dorsal  surface  of  the  posterior  part 
of  the  left  lobe  of  the  liver,  where  it  extends  almost  to  the  gall  bladder 
(Holmes,  p.  151). 

6.  The  bile  duct. — The  common  bile  duct  runs  through  the  pancreas  and 
enters  the  duodenum  by  way  of  the  second  of  the  tail-like  processes  mentioned 
above,  i.e.,  the  one  farthest  away  from  the  pylorus.     Dissect  away  the  pancreas 
in  this  region,  and  find  the  slender  white  duct,  about  the  size  of  a  sewing  thread 
Trace  the  duct  up  through  the  pancreas  into  the  hepatic  process  of  the  pancreas. 
Here  it  receives  a  number  of  small  hepatic  ducts  from  the  posterior  part  of  the 
left  lobe.     To  find  these  dissect  away  the  substance  of  the  liver.     Follow  the 
bile  duct  to  the  gall  bladder,  where  it  again  receives  hepatic  ducts  from  the  right 
lobe  and  the  posterior  part  of  the  left  lobe.     Two  ducts,  the  cystic  ducts,  emerge 
from  the  gall  bladder.     One  of  them  unites  with  the  hepatic  ducts  near  by,  and 
the  other  is  continuous  with  the  common  bile  duct.     Consult  Holmes,  Fig.  42, 
p.  152,  and  work  out  the  hepatic  and  cystic  ducts  as  well  as  you  can.     It  is  not 
practical  to  find  the  pancreatic  ducts. 

7.  The  large  intestine. — The  ileum  enlarges  abruptly  into  the  large  intestine, 
which  runs  straight  to  the  anus.    The  upper  part  of  the  large  intestine  is  called 
rectum;  the  lower  part,  cloaca.     Cut  through  the  pelvic  girdle  so  as  to  expose 
the  intestine  all  the  way  to  the  anus.     Find  the  origin  of  the  urinary  bladder 
from  the  ventral  wall  of  the  cloaca.     The  cloaca  also  receives  the  ureters  and 
oviducts. 

Draw  the  entire  digestive  tract,  showing  all  its  parts,  with  the  lobes  of  the 
liver  turned  forward.  Draw  in  the  common  bile  duct  in  proper  position  in  the 
pancreas,  and  the  hepatic  and  cystic  ducts  as  far  as  you  have  been  able  to  find 
them. 

B.      THE  URTNOGENITAL  SYSTEM 

Remove  the  digestive  system,  leaving  the  large  intestine  in  place  (Holmes, 
chap,  xi,  pp.  212-18). 

i.  Male  urinogenital  system. — Strip  off  the  peritoneum  wherever  necessary 
to  expose  the  urinogenital  system.  Each  testis  is  an  oval  body  attached  by  a 
fold  of  peritoneum,  the  mesorchium,  to  the  adjacent  kidney.  From  each  testis 
spring  several  delicate  ducts,  the  vasa  efferentia,  which  run  in  the  mesorchium 
and  penetrate  the  kidney.  The  vasa  efferentia  are  really  outgrowths  of  the 
Malpighian  bodies  of  the  kidney,  which  extend  out  and  connect  with  the  testes. 
By  holding  up  the  mesorchium  to  the  light,  the  vasa  efferentia  may  usually  be 
seen.  The  vasa  efferentia  after  entering  the  kidney  eventually  connect  with  the 
ureter  by  a  route  which  differs  in  different  species  of  frogs.  From  the  posterior, 
lateral  edge  of  each  kidney  extends  the  ureter.  Find  it  and  trace  it  to  the  cloaca. 
Alongside  and  parallel  to  the  lateral  edge  of  the  kidney  runs  a  vestigial  oviduct, 


THE  SPECIAL  ANATOMY  OF  THE  FROG  41 

which  also  opens  into  the  cloaca.  Trace  it  to  the  cloaca  and  note  that  the  ureter 
is  closely  applied  to  the  dorsal  side  of  the  oviduct. . 

Draw  the  male  urinogenital  system  showing  all  of  the  above-mentioned  parts. 

2.  Female  urinogenital  system. — The  relations  of  kidney  and  ureter  are  the 
same  as  in  the  male.  The  ovary,  however,  bears  no  relation  to  the  kidney. 
It  and  its  mesentery  have  already  been  noted.  The  oviducts  are  a  pair  of  con- 
voluted tubes,  extending  the  whole  length  of  the  body  cavity.  Trace  one 
anteriorly  to  the  anterior  wall  of  the  coelome,  where  it  opens  into  the  body 
cavity  by  a  funnel-shaped  mouth,  or  ostium,  near  the  base  of  the  lung.  Have  the 
assistant  demonstrate  .the  ostium  to  you.  Trace  the  oviduct  posteriorly  to  the 
cloaca.  It  widens  into  a  large,  thin-walled  sac,  the  uterus,  which  lies  behind 
(dorsal  to)  the  peritoneum  in  the  cisterna  magna.  Cut  open  the  cloaca,  and 
locate  in  its  'dorsal  wall  the  two  openings  of  the  oviducts,  situated  upon  pro- 
jecting papillae  and  in  the  ventral  wall,  the  opening  of  the  urinary  bladder. 

Draw  the  female  urinogenital  system  with  the  cloaca  cut  open,  showing  all 
parts. 

C.      THE  RESPIRATORY  SYSTEM 

At  their  anterior  ends  the  two  lungs  open  into  a  chamber,  the  larynx,  which 
communicates  with  the  pharynx  through  the  slitlike  glottis.  The  larynx  lies 
just  in  front  of  the  heart.  Consult  Holmes,  chapter  viii,  pp.  165-68.  Dissect 
away  all  the  muscles  from  the  under  surface  of  the  lower  jaw  so  as  to  expose  the 
flat  body  of  the  hyoid  cartilage.  Find  the  two  thyroid  processes  of  the  hyoid 
which  extend  posteriorly  and  inclose  the  laryngeal  chamber  between  them.  The 
walls  of  this  chamber  are  supported  by  a  complicated  arrangement  of  cartilages 
for  which  Holmes,  Fig.  45  (p.  166),  should  be  consulted.  Dissect  posteriorly 
from  the  larynx  and  remove  or  cut  through  blood  vessels  or  other  structures 
until  you  have  exposed  the  connection  of  the  lungs  with  the  larynx.  Make  a 
longitudinal  slit  through  the  ventral  wall  of  the  larynx,  spread  the  sides  apart 
and  look  within  for  the  weal  cords,  a  pair  of  folds  extending  lengthwise  in  the 
chamber.  Find  the  openings  of  the  lungs  into  the  latero-posterior  walls  of  the 
larynx,  insert  one  blade  of  a  scissors  into  one  of  the  openings  and  slit  open  the 
wall  of  the  lung.  Note  that  the  inner  wall  of  the  lung  is  raised  up  into  a  network 
of  ridges,  which  divide  the  wall  into  a  large  number  of  small  chambers  or  alveoli. 
Blood  vessels  run  along  the  ridges  and  break  up  into  an  intricate  network  of 
capillaries  in  the  walls  of  each  alveolus,  which  serves  as  an  air  sac. 

Draw  the  dissection. 

D.      THE    CIRCULATORY  SYSTEM:     THE   VENOUS   SYSTEM 

For  this  purpose  a  fresh  frog,  probably  injected,  will  be  supplied.  Open  it 
up  in  the  usual  way  to  the  left  of  the  median  line,  but  be  very  careful  not  to  cut 
any  blood  vessels,  especially  near  the  heart.  Be  very  cautious  in  spreading  the 


42  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

body  walls  apart  near  the  heart,  so  as  not  to  injure  the  veins.  The  anterior 
abdominal  vein  in  the  median  ventral  line  must  be  preserved  and  should  be 
separated  from  the  body  wall  before  spreading  the  walls  apart. 

i.  The  systemic  veins  (Holmes,  pp.  272-74).— Systemic  veins  are  those  which 
open  into  the  heart,  returning  blood  from  the  body  directly  to  the  heart.  Remove 
the  pericardial  sac  from  the  heart,  and  turn  the  heart  forward  so  as  to  expose  the 
sinus  venosus.  Three  large  veins  contribute  to  the  sinus  venosus:  the  posterior 
vena  cava,  or  postcaval  vein,  which  emerges  from  the  liver  (receiving  a  large  vein 
on  each  side  from  the  liver  so  that  apparently  three  veins  are  present)  and  enters 
the  median  posterior  wall  of  the  sinus;  and  the  two  anterior  venae  cavae,  or 
precaval  veins,  one  opening  into  each  lateral  wall  of  the  sinus. 

a)  The  precaval  vein:  Trace  one  of  the  precaval  veins  (since  both  have  iden- 
tical branches).     It  extends  laterally  from  the  heart  along  the  border  of  the 
auricle,  and  about  i  cm.  away  from  the  heart  passes  through  the  pleuro- 
peritoneal  membrane.     Directly  outside  of  this  membrane  it  forks  simulta- 
neously into  three  branches.     The  most  anterior  one  of  these  is  the  external 
jugular;  it  passes  straight  anteriorly  into  the  muscles  of  the  floor  of  the  mouth, 
from  which,  together  with  the  tongue,  hyoid,  etc.,  it  receives  venous  blood 
through  numerous  small  branches.     The  middle  of  the  three  branches  of  the 
precaval  is  the  inominate;  it  passes  laterally  and  then  turns  abruptly  dorsally, 
receiving  as  it  turns  a  small  subscapular  vein  from  the  muscles  of  the  shoulder. 
The  main  vein  beyond  the  entrance  of  this  branch  is  known  as  the  internal 
jugular;   it  descends  straight  into  the  hollow  between  the  fore  limb  and  the 
larynx,  and  disappears  dorsally  where  it  collects  blood  from  the  brain  and  spinal 
cord,  from  the  roof  of  the  mouth,  and  from  a  number  of  muscles.    The  third  and 
posterior  branch  of  the  precaval  is  the  subclavian.    It  is  a  large  vein  passing 
directly  laterally  to  the  base  of  the  fore  limb  where  it  receives  the  brachial  vein, 
carrying  venous  blood  out  of  the  fore  limb.     Just  beyond  this  point  the  vein, 
now  called  cutaneous^  or  musculo-cutaneous,  turns  abruptly  and  runs  straight 
posteriorly  along  the  muscle  of  the  ventro-lateral  body  wall  (pectoral  muscle). 
It  then  bends  sharply  dorsally  and  passes  to  the  skin  by  way  of  the  partition 
between  the  abdominal  and  lateral  lymph  sacs.     It  runs  anteriorly  under  the 
skin  forward  to  the  nares,  collecting  venous  blood  from  the  skin  of  the  entire 
dorsal  side. 

b)  The  postcaval  vein:  Trace  the  postcaval  posteriorly  from  the  sinus  venosus 
into  the  liver.    Where  it  emerges  from  the  liver  substance  it  receives  two  large 
hepatic  veins,  one  from  the  right  lobe,  the  other  from  the  left  lobe  of  the  liver. 
Turn  the  lobes  of  the  liver  to  the  right  and  find  where  the  postcaval  enters  the 
middle  lobe  from  behind.     Trace  it  posteriorly.     It  originates  between  the  two 
kidneys,  from  which  it  receives  a  number  of  renal  veins  as  well  as  veins  from  the 
reproductive  organs  and  fat  bodies. 


THE  SPECIAL  ANATOMY  OF  THE  FROG 


43 


2.  The  hepatic  portal  system  (Holmes,  p.  277). — A  portal  system  is  one  in 
which  the  venous  blood  does  not  return  directly  to  the  heart  but  enters  a  system 
of  capillaries  in  some  organ  from  which  the  venous  blood  is  then  collected  by  a 
systemic  vein.     There  are  two  portal  systems  in  the  frog,  the  hepatic  portal  sys- 
tem in  which  the  interposed  capillaries  are  in  the  liver,  and  the  renal  portal  system 
where  they  are  in  the  kidney.     Spread  out  the  liver   with  its  lobes   turned 
forward  so  that  the  pancreas  is  visible.     Find  a  large  vein  ascending  through 
the  substance  of  the  pancreas  and  forking  on  the  dorsal  surface  of  the  liver. 
This  is  the  hepatic  portal  vein  which  breaks  up  into  a  system  of  capillaries 
in  the  liver.     The  left  fork  of  the  hepatic  portal  vein  sinks  into  the  substance 
of  the  posterior  part  of  the  left  lobe  of  the  liver.     The  right  fork  connects 
with  the   anterior  abdominal  vein  which  also   forks  and  then  penetrates  the 
liver.     Trace  the  hepatic  portal  vein  posteriorly  and  note  that  it  is  formed 
by  the  union  of  veins  from   the  stomach,  pancreas,  spleen,  and   small'  and 
large  intestines.    All  of  the  blood  from  the  digestive  tract  therefore  enters  a 
capillary  system  in  the  liver,  from  which  it  flows  into  the  postcaval  vein  by 
way  of  the  hepatic  veins.     What  is  the  purpose  of  this  arrangement?     Consult 
Holmes,  p.  153. 

3.  The  renal  portal  system. — Expose  the  kidneys  and  find  along  the  outer 
lateral  edge  of  each  a  conspicuous  vein,  the  renal  portal  vein,  which  enters  the 
substance  of  the  kidney.     Trace  the  renal  portal  vein  posteriorly.     At  about  the 
middle  of  the  kidney  it  receives  a  vein,  the  dor  so-lumbar  vein,  from  the  muscles 
of  the  back.    Posterior  to  the  kidney  it  is  seen  to  be  formed  from  two  veins 
which  come  from  the  leg.     The  outer  of  the  two  veins  is  the  femoral,  the  inner, 
the  sciatic.    At  the  point  where  each  femoral  vein  enters  the  coelome,  it  gives 
off  a  branch,  the  pelvic  vein,  which  runs  along  the  posterior  wall  of  the  coelome 
to  the  median  line  where  it  joins  the  other  pelvic.     This  union  of  the  two  pelvic 
veins  produces  the  abdominal  vein,  which  joins  the  hepatic  portal  vein  as 
described  above.     The  abdominal  vein  is  thus  a  connection  between  the  renal 
and  hepatic  portal  systems,  and  blood  from  the  hind  legs  may  return  to  the 
heart  either  by  way  of  the  kidneys  or  by  way  of  the  liver.     In  the  kidneys  the 
renal  portal  vein  breaks  up  into  capillaries,  from  which  the  blood  is  collected  by 
the  postcaval  vein. 

4.  The  pulmonary  veins. — From  each  lung  a  pulmonary  vein  passes  dorsal 
to  the  sinus  venosus  and  enters  the  left  auricle.     These  veins  are  sometimes 
difficult  to  locate.     Turn  the  heart  forward  holding  it  down  with  the  finger  so 
that  it  will  be  stretched.     Pull  away  with  a  forceps  the  coronary  ligament  of 
the  liver  so  as  to  expose  the  lungs.     A  short  straight  vessel  will  be  found  running 
from  the  inner  border  of  the  base  of  each  lung  obliquely  toward  the  sinus  venosus. 
These  two  pulmonary  veins  join  just  under  the  beginning  of  the  left  precaval  vein 
and  penetrate  the  left  auricle  at  that  point. 


44  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

Make  an  outline  drawing  of  the  frog  and  its  organs,  and  in  this  put  the 
venous  system  in  its  proper  relations  to  the  organs.  More  than  one  drawing  may 
be  necessary.  Draw  only  those  vessels  which  you  have  found. 


E.      THE    CIRCULATORY  SYSTEM:    THE  ARTERIAL   SYSTEM 

The  conus  arteriosus  starts  from  the  base  of  the  right  side  of  the  ventricle, 
passes  obliquely  across  the  auricles,  and  divides  near  the  anterior  border  of  the 
auricles  into  two  vessels  which  turn  respectively  to  the  right  and  left.  Each 
branch  is  called  a  truncus  arteriosus  and  each  gives  rise  shortly  to  three  arteries, 
which  are  designated  as  aortic  or  arterial  arches.  To  find  this  division  into  three, 
carefully  pick  off  the  connective  tissue,  etc.,  from  the  surface  of  one  truncus,  and 
follow  it  away  from  the  heart.  The  most  anterior  of  the  three  arches  is  the 
carotid  arch;  the  middle  one  is  the  systemic  arch;  the  most  posterior,  the  pulmo- 
cutaneous  arch.  The  pulmo-cutaneous  arch  generally  branches  off  before  the 
other  two  (Holmes,  pp.  268-70). 

1.  The  carotid  arch. — This  vessel  passes  forward  and  soon  divides  into  two 
branches,  a  medial  small  external  carotid,  and  a  lateral  larger  internal  carotid. 
Just  at  the  place  of  division,  or  situated  on  the  internal  carotid,  is  an  enlarge- 
ment, the  carotid  gland,  presenting  a  blackish  appearance  owing  to  the  presence 
of  pigment  cells.     The  internal  carotid  supplies  the  roof  of  the  mouth,  eye,  brain, 
and  spinal  cord.     The  external  carotid  (or  lingual)  supplies  the  tongue,  thyroid, 
and  various  muscles.     Trace  the  branches  of  the  carotid  arch  as  far  as  practicable. 

2.  The  pulmo-cutaneous  arch. — Trace  this  out  from  the  truncus  arteriosus, 
and  note  that  it  soon  divides  into  two  branches.     One  of  these,  the  pulmonary, 
is  short,  and  runs  directly  to  the  lung.     The  other,  the  cutaneous,  passes  outward 
and  forward,  crossing  the  systemic  arch,  and  then  by  a  sharp  dorsal  turn  dis- 
appears in  front  of  the  shoulder.     Turn  the  frog  dorsal  side  up,  slit  up  the  skin 
of  the  back,  and  deflect  it.     Find  where  the  cutaneous  artery  emerges  just  in 
front  of  the  suprascapula,  and  note  its  branches  on  the  skin. 

3.  The  systemic  arch. — The  systemic  arch  passes  laterally  and  forward,  and 
seems  to  disappear  in  the  mass  of  muscles.     Dissect  away  these  muscles  and 
follow  its  course.     It  runs  forward  alongside  the  internal  carotid,  then  bends 
dorsally  and  turns  backward  dorsal  to  the  esophagus.    Just  after  it  has  made 
this  posterior  turn,  the  systemic  arch  gives  rise  to  the  following  branches  prac- 
tically simultaneously:    the  small  esophageal  arteries,  which  supply  the  esoph- 
agus;   the  subclavian,  which  passes  laterally  to  the  foreleg;  and  the  occipito- 
vertebral,  which  passes  dorsally  and  promptly  divides  into  an  anterior  branch, 
the  occipital,  and  a  posterior  branch,   the  vertebral.     Both  of  these  can  be 
readily  followed  in  well-injected  specimens.     Turn  the  frog  dorsal  side  up, 
and  find  the  occipital  artery  emerging  just  under  the  anterior  border  of  the 
suprascapula.     Follow  it  along  the  head,  noting  a  branch  above  the  eye  to  the 


THE  SPECIAL  ANATOMY  OF  THE  FROG  45 

anterior  parts  of  the  head,  and  one  behind  the  eye  for  the  upper  and  lower  jaws. 
Remove  all  muscles  from  the  vertebral  column,  and  note  the  intricate  branches 
of  the  vertebral  artery  to  the  vertebrae. 

The  two  systemic  arches  from  the  two  sides  of  the  body  now  converge  and 
unite  to  form  a  single  large  vessel,  the  dorsal  aorta.  The  dorsal  aorta  lies  in  the 
cisterna  magna,  above  the  kidneys,  and  the  pleuroperitoneum  must  be  broken 
through  in  the  usual  way  to  one  side  of  one  of  the  kidneys  in  order  to  follow  this 
vessel.  At  the  point  of  union  of  the  systemic  arches,  the  large  coeliaco-mesenteric 
artery  arises.  Trace  the  branches  of  this  artery.  It  divides  into  a  coeliac, 
which  supplies  the  stomach,  pancreas,  and  liver  (right  and  left  gastric  arteries, 
and  hepatic  artery),  and  an  anterior  mesenteric,  which  gives  off  a  short  branch 
to  the  spleen  (lienal  artery),  a  number  of  branches  to  the  small  intestine  (intes- 
tinal arteries),  and  one  or  more  branches  to  the  large  intestine  (anterior  haemor- 
rhoidal  arteries). 

Posterior  to  the  origin  of  the  coeliaco-mesenteric,  the  dorsal  aorta  gives  rise 
to  a  number  of  small  paired  urino genital  arteries,  which  supply  mainly  the  kid- 
neys, but  branch  also  to  the  fat  bodies,  and  reproductive  organs  and  their  ducts. 
In  the  same  region,  one  to  four  pairs  of  small  lumbar  arteries  arise  from  the  aorta 
and  pass  to  the  dorsal  body  wall. 

The  dorsal  aorta  next  gives  off  a  single  median  branch,  the  posterior  mesenteric, 
to  the  large  intestine,  and  shortly  after  this  bifurcates  into  two  large  arteries,  the 
common  iliac  arteries.  Each  common  iliac  soon  gives  rise  to  two  branches.  One 
of  these,  the  epigastrico-Desical  artery,  branches  almost  immediately  into  an 
epigastric  artery  for  the  muscles  of  the  lateral  and  ventral  abdominal  walls,  and 
a  recto-vesical  artery  for  the  urinary  bladder  and  the  rectum.  The  other  is  a 
small  artery  to  the  urinogenital  ducts.  The  iliac  then  supplies  a  small  femoral 
artery  for  the  muscles  of  the  thigh  and  continues  down  the  leg  as  a  large  vessel, 
the  sciatic  artery. 

Make  an  outline  of  the  frog  and  its  organs  and  put  in  the  arteries,  showing 
their  proper  location  and  distribution.  All  of  the  arteries  mentioned  can  be 
readily  found  in  well-injected  specimens.  Omit  those  that  you  could  not  identify. 

Be  able  to  trace  the  blood  from  any  part  to  any  other  part. 

F.      THE    CIRCULATORY  SYSTEM:     THE   STRUCTURE   OF  THE  HEART 

The  four  parts  of  the  heart,  the  sinus  venosus,  the  auricles,  the  ventricle,  and 
the  conus  arteriosus,  have  already  been  noted.  Draw  the  heart  from  the  side; 
show  these  parts. 

The  dissection  of  the  heart  should  not  be  attempted  except  upon  a  well- 
preserved,  uninjured  heart.  The  heart  of  injected  specimens  cannot  be  used 
(Holmes,  pp.  64-68).  With  a  fine  scissors  remove  the  ventral  wall  of  the  ven- 
tricle, the  ventral  wall  of  each  auricle,  and  the  ventral  wall  of  the  conus  arteriosus 


46  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

as  far  as  the  forking  of  the  trunci  arteriosi.  If  desirable  the  heart  may  be  removed 
from  the  body  by  cutting  through  the  aortic  arches  and  the  sinus  venosus;  then 
mount  the  heart  under  water  in  a  small  wax-bottomed  dish.  Note  the  thick 
spongy  walls  of  the  ventricle  and  its  small  central  cavity.  Find  the  openings 
of  the  two  auricles  into  the  ventricle.  The  walls  of  the  auricles  are  quite  thin 
and  the  right  one  is  considerably  larger  than  the  left.  The  large  opening  of 
the  sinus  venosus  into  the  right  auricle  is  readily  found.  The  conus  arteriosus 
contains  a  conspicuous  structure,  the  spiral  valve,  which  almost  fills  its  cavity. 
It  is  a  fold,  bent  slightly  into  an  S-shape,  extending  lengthwise  in  the  conus,  its 
dorsal  edge  attached  along  the  entire  extent  of  the  dorsal  wall  of  the  conus,  its 
ventral  margin  free.  In  the  cross-section  of  the  truncus  arteriosus  observe  the 
two  partitions  which  divide  it  into  three  channels,  one  for  each  aortic  arch. 
The  ventral  channel  leads  to  the  carotid  arch,  and  the  middle  one  to  the  systemic 
arch;  the  beginnings  of  these  two  channels  are  in  the  conus  arteriosus  in  front 
of  the  termination  of  the  spiral  valve,  so  that  the  blood  to  reach  them  must  flow 
over  the  cuplike  widened  anterior  end  of  the  valve.  The  dorsal  channel  of  the 
truncus  arteriosus  passes  into  the  pulmo-cutaneous  arch;  it  starts  farther  down 
in  the  conus  below  the  anterior  end  of  the  spiral  valve,  so  that  blood  reaches  it 
by  flowing  over  the  free  ventral  edge  of  the  valve.  Read  Holmes,  pp.  277-79, 
and  understand  the  function  of  the  spiral  valve  and  the  partitions  in  the  truncus 
arteriosus  in  directing  the  venous  blood  into  the  pulmo-cutaneous  arch,  mixed 
blood  into  the  systemic  arches,  and  the  arterial  blood  into  the  carotid  arch. 
Draw  the  dissection  from  the  ventral  side. 


G.      THE  NERVOUS   SYSTEM 

Remove  the  skin  and  clean  away  all  muscles  from  the  median  dorsal  region 
of  the  animal.  With  a  fine  scissors  and  forceps  remove  the  roof  of  the  skull 
bit  by  bit,  being  careful  to  keep  the  point  of  the  scissors  well  up  against  the 
bone  so  as  not  to  jab  into  the  soft  brain  tissue.  First  cut  into  the  bone,  then 
pull  away  the  pieces  with  the  forceps.  Remove  the  roof  as  far  forward  as  the 
nares.  Next  work  posteriorly  in  the  same  way.  Cut  through  the  neural  arches 
of  the  vertebrae  by  lateral  cuts,  and  pull  out  the  central  piece  with  the  forceps. 
The  brain  and  cord  should  bt  well  exposed  before  their  study  is  undertaken 
(Holmes,  chap,  xvi,  pp.  283-95). 

i.  Dorsal  aspect  of  the  brain  (Holmes,  pp.  291-95). — The  brain  is  covered 
with  a  pigmented  membrane,  the  pia  mater,  which  is  particularly  abundant  in 
the  posterior  part  of  the  brain,  where  it  is  very  vascular  and  fills  a  triangular 
cavity,  the  fourth  ventricle.  The  pia  mater  should  be  removed  from  the  fourth 
ventricle. 

The  most  anterior  part  of  the  brain  comprises  a  pair  of  rounded  olfactory 
lobes,  which  are  separated  from  each  other  by  a  faint  median  groove.  Each 


THE  SPECIAL  ANATOMY  OF  THE  FROG  47 

olfactory  lobe  continues  forward  to  the  nasal  sac  as  the  olfactory  nerve.  The 
posterior  boundary  of  the  olfactory  lobes  is  marked  by  a  transverse  groove  which 
separates  them  from  the  next  part  of  the  brain,  a  pair  of  long  oval  bodies,  the 
cerebral  hemispheres.  Just  behind  the  cerebral  hemispheres  is  a  depressed  region, 
the  diencephalon  or  thalamencephalon,  from  which  a  delicate  stalklike  body,  the 
pineal  body,  ascends  dorsally  to  the  brow  spot.  The  pineal  body  is  almost  always 
torn  off  in  removing  the  skull  and  hence  cannot  be  seen.  Posterior  to  the 
diencephalon  are  the  two  rounded  optic  lobes.  Just  behind  them  and  forming 
the  anterior  wall  of  the  triangular  cavity  of  the  fourth  ventricle  is  the  cerebellum. 
This  is  much  smaller  in  the  frog  than  in  most  other  vertebrates.  The  region 
of  the  brain  posterior  to  the  cerebellum,  and  forming  the  floor  and  lateral  walls 
of  the  fourth  ventricle  is  known  as  the  medulla  oblongata.  It  narrows  posteriorly 
until  it  becomes  of  the  same  width  as  the  spinal  cord  with  which  it  is  continuous. 

2.  THe  cranial  nerves  (Holmes,  p.  295). — Ten  pairs  of  nerves  spring  from 
the  lateral  and  ventral  surfaces  of  the  brain  but  most  of  these  cannot  be  found 
unless  very  great  care  is  exercised  in  dissecting.     The  first  pair  of  cranial  nerves, 
the  olfactory,  has  already  been  noted  arising  from  the  olfactory  lobes.    The 
second  pair  of  nerves,  the  optic  nerves,  springs  from  the  ventral  surface  of  the 
diencephalon,  and  may  be  seen  by  gently  pushing  this  part  of  the  brain  to  one 
side.     Each  penetrates  the  adjacent  eyeball  where  it  forms  the  retina.    The 
third,  fourth,  and  sixth  nerves  are  motor  nerves  to  the  muscles  of  the  eyeball 
and  are  too  small  to  be  found.     The  fifth,  seventh,  and  eighth  nerves  arise  close 
together  from  the  side  of  the  anterior  end  of  the  medulla,  and  may  usually  be 
seen  by  gently  pressing  back  this  region.     The  ninth  and  tenth  arise  together 
from  the  side  of  the  medulla  a  short  distance  behind  the  eighth. 

3.  The  spinal  cord. — The  spinal  cord  is  continuous  with  the  medulla  oblongata 
and  occupies  a  cavity  within  the  vertebral  column  known  as  the  neural  canal. 
Posteriorly  the  spinal  cord  tapers  into  a  fine  thread,  the  filum  terminate,  which 
occupies  the  cavity  of  the  urostyle  and  can  be  seen  by  cutting  off  the  dorsal  half 
of  the  urostyle.     The  spinal  cord  is  slightly  enlarged  opposite  the  fore  limb 
(brachial  enlargement)  and  again  anterior  to  the  filum  terminale  (sciatic  enlarge- 
ment).   These  swellings  are,  of  course,  caused  by  the  origin  of  the  nerves  to  the 
limbs  at  those  regions.     In  the  median  dorsal  line  of  the  cord  is  a  longitudinal 
groove,  the  dorsal  fissure.    In  a  well-dissected  specimen,  the  dorsal  roots  of  the 
spinal  nerves  may  be  seen  arising  at  regular  intervals  from  the  dorso-lateral 
region  of  the  cord.     The  posterior  roots  run  within  the  neural  canal  for  a  little 
distance  alongside  the  spinal  cord  before  passing  out  of  the  vertebral  column. 

Draw  the  brain  and  cord  from  the  dorsal  side. 

4.  Ventral  aspect  of  the  brain. — Cut  across  the  cord  back  of  the  medulla 
oblongata,  and  carefully  remove  the  brain,  leaving  the  cord  in  place.     In  remov- 
ing the  brain  note  and  cut  through  the  more  conspicuous  of  the  cranial  nerves. 
Study  the  ventral  surface  of  the  brain  and  identify  the  parts  already  noted  on 


48  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

the  dorsal  side.  On  the  ventral  side  of  the  diencephalon  observe  the  crossing 
of  the  optic  nerves,  after  their  origin  from  the  diencephalon;  this  crossing  is 
called  the  optic  chiasma.  Just  behind  the  optic  chiasma  is  a  bilobed  extension 
of  the  floor  of  the  diencephalon,  called  the  inferior  lobes  or  infundibulum;  and 
to  this  is  attached  a  rounded  glandular  body,  the  hypophysis,  which  fits  into  a 
depression  in  the  floor  of  the  skull,  and  is  usually,  therefore,  torn  off  in  removing 
the  brain.  The  hypophysis  is  a  gland  of  internal  secretion. 
Draw  the  ventral  surface  of  the  brain. 

5.  The  ventricles  of  the  brain. — The  brain  like  the  spinal  cord  is  hollow,  its 
cavity  being  continuous  with  the  central  canal  of  the  cord.    The  cavities  of  the 
brain  are  known  as  ventricles.    Make  a  median  sagittal  section  of  the  brain, 
float  it  under  water,  and  identify  the  ventricles.     See  also  Holmes,  Fig.  83 
(p.  292),  and  Fig.  84  (p.  293).    The  cavity  of  the  medulla  oblongata  is  the  largest 
and  most  posterior  of  the  ventricles ;  it  is  called  the  fourth  ventricle  and  has  a 
thin  vascular  roof  which  has  already  been  removed.     From  the  fourth  ventricle 
a  narrow  passage,  the  iter  or  aqueduct  of  Sylvius,  extends  forward  below  the  optic 
lobes.     Each  optic  lobe  has  a  cavity,  the  optic  ventricle.     The  ventricle  of  the 
diencephalon  which  extends  downward  into  the  infundibulum  is  the  third  ven- 
tricle.    The  first  and  second  ventricles,  also  called  the  lateral  ventricles,  are 
inside  of  the  cerebral  hemispheres,  which  should  be  cut  open  to  see  them.     The 
narrow  passage  which  connects  the  lateral  with  the  third  ventricles  is  known  as 
the  foramen  of  Monro. 

6.  The  spinal  nerves  (Holmes,  pp.  89-91). — Turn  the  frog  ventral  side  up, 
and  remove  all  the  viscera.     Observe  the  spinal  nerves  passing  out  symmetrically 
from  the  sides  of  the  vertebral  column.     They  arise  from  the  cord  and  leave  the 
neural  canal  by  way  of  openings  (intervertebral  foramina)  between  the  vertebrae. 
There  are  ten  pairs  of  spinal  nerves,  each  of  which  divides  immediately  into  a 
small  dorsal  branch  and  a  larger  ventral  branch.     It  is  the  ventral  branch  which 
one  sees  running  on  the  inside  of  the  dorsal  body  wall.     At  the  point  of  exit  of 
each  spinal  nerve  from  the  intervertebral  foramen  is  a  white  mass,  the  calcareous 
body,  which  surrounds  and  conceals  a  ganglion. 

Identify  and  observe  the  course  of  each  of  the  spinal  nerves.  The  first  is 
quite  small;  it  arises  between  the  first  and  second  vertebrae  and  innervates  the 
tongue  and  muscles  of  the  hyoid.  The  second  is  a  large  stout  nerve  which 
innervates  the  muscles  of  the  fore  limb.  It  is  joined  by  branches  of  the  first 
and  third  spinal  nerves,  and  all  of  these  together  form  a  network  which  is  called 
the  brachial  plexus.  The  presence  of  such  a  plexus  indicates  the  compound 
origin  of  the  muscles  of  the  limb.  The  fourth,  fifth,  and  sixth  nerves  are  small 
and  pass  somewhat  obliquely  backward  to  supply  the  skin  and  muscles  of  the 
body  wall.  The  seventh,  eighth,  ninth,  and  tenth  nerves  arise  close  together, 
run  almost  directly  backward,  and  are  united  with  one  another  by  cross  branches 
to  form  the  sciatic  plexus  from  which  nerves  go  to  the  muscles  and  skin  of  the 


THE  SPECIAL  ANATOMY  OF  THE  FROG  49 

hind  limbs.     The  small  tenth  nerve  arises  from  the  urostyle,  and  innervates 
mainly  the  cloaca,  and  urinary  bladder. 

Draw  the  spinal  nerves  as  seen  on  the  dorsal  body  wall. 

7.  The  roots  of  the  spinal  nerves. — Select  one  of  the  largest  spinal  nerves 
(as  the  eighth),  and  trace  it  carefully  into  the  vertebral  column,  cutting  away  the 
vertebrae.     Pull  off  the  calcareous  body  and  find  within  it  a  small  brown  object, 
the  dorsal  or  spinal  ganglion.     (The  term  "ganglion"  means  a  mass  of  nerve 
cell  bodies  lying  outside  of  the  brain  and  spinal  cord.)     Tracing  the  nerve  farther 
in  toward  the  cord  note  that  it  divides  into  two  branches  or  roots,  one  of  which 
is  attached  to  the  dorso-lateral  region  of  the  cord,  the  other  to  the  ventro- 
lateral  region.     These  roots  are  designated  as  the  dorsal  and  ventral  roots.    The 
dorsal  root  springs  from  the  dorsal  horn  of  the  gray  matter  of  the  cord;  it  carries 
sensory  fibers  which  arise  from  the  nerve  cells  located  in  the  dorsal  ganglion. 
The  ventral  root  takes  its  origin  from  the  ventral  horn  of  the  gray  matter,  from 
the  large  motor  cells  which  have  already  been  seen  in  that  location,  and  carries 
motor  fibers  to  the  muscles.     The  two  roots  meet  just  beyond  the  spinal  ganglion, 
which  is  on  the  dorsal  root,  and  the  spinal  nerve  thus  formed  soon  divides  into 
dorsal  and  ventral  branches  or  rami,  as  noted  in  the  preceding  section.    Each 
ramus  carries  both  sensory  and  motor  fibers  and  supplies  both  skin  and  muscles; 
and  the  ventral  ramus  is  further  connected  by  the  ramus  communicans  with  the 
sympathetic  system. 

Make  a  diagram  to  show  the  origin  of  a  spinal  nerve  from  the  cord. 

8.  General  remarks  on  the  function  of  the  brain  and  cord. — The  possibility 
that  any  organism  born  into  the  conditions  of  life  as  they  exist  upon  the  earth 
will  survive  depends  entirely  upon  its  ability  to  perceive  and  respond  effectively 
to  those  conditions.     We  have  already  found  that  this  capacity  for  the  percep- 
tion of  conditions  in  the  environment  and  for  responding  to  them  is  vested  in  the 
nervous  system.     The  perceiving  part  of  the  apparatus  is  the  sense  organs, 
which  comprise  the  eye,  ear,  and  nose,  taste  organs  in  the  mouth,  organs  of 
touch,  pressure,  pain,  temperature,  chemical  sense,  etc.,  in  the  skin,  and  sensory 
organs  in  the  viscera.     The  responding  part  of  the  apparatus  is  the  brain  and 
cord  through  the  motor  nerves  to  muscles  and  glands. 

In  a  prone  animal  moving  with  one  end  forward,  that  end  will  come  first  in 
contact  with  the  factors  of  the  environment  and  hence  will  naturally- come  to 
be  the  place  where  the  most  important  and  specialized  sense  organs  are  located. 
Further,  the  part  of  the  nervous  system  connected  with  these  important  sense 
organs  must  become  enlarged  to  accommodate  the  numerous  impulses  sent  in 
from  them,  and  must  thus  acquire  dominance  over  the  rest  of  the  central  nervous 
system.  We  may  thus  account  for  the  origin  of  the  head  and  brain,  which 
structures  indeed  made  their  appearance  in  the  simplest  bilateral  animals. 

We  therefore  find  that  the  brain  of  a  relatively  simple  vertebrate  like  the 
frog  consists  in  large  part  of  centers  for  the  reception  of  the  chief  sensations. 

5 


50  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

Thus  the  olfactory  lobes,  the  larger  part  of  the  cerebral  hemispheres,  and  the 
dorsal  and  ventral  parts  of  the  diencephalon  are  olfactory.  The  lateral  walls  of 
the  diencephalon  and  part  of  the  optic  lobes  are  the  receptive  regions  for  vision. 
Another  part  of  the  optic  lobes  and  the  dorsal  margins  of  the  anterior  end  of  the 
medulla  are  the  centers  of  hearing.  The  general  sensations  from  the  skin  of  the 
body  are  received  into  the  dorsal  regions  of  the  spinal  cord,  which  extend  forward 
to  the  same  regions  of  the  medulla,  where  similar  sensations  from  the  head  also 
enter.  The  dorsal  and  lateral  regions  of  the  medulla,  therefore,  together  with 
the  same  regions  of  the  optic  lobes  and  diencephalon  are  centers  of  general 
sensations.  Taste  and  other  visceral  sensations  are  received  in  the  ventro- 
lateral  regions  of  the  medulla.  The  ventral  portions  of  the  brain  from  the 
optic  lobes  posteriorly  and  down  the  whole  length  of  the  cord  in  the  ventral 
horns  of  the  gray  matter  are  the  regions  of  origin  of  motor  impulses. 

Obviously  these  primary  sense  centers  must  be  connected  with  the  motor 
nerve  cells  from  which  nerves  go  to  the  muscles  in  order  that  an  appropriate 
response  may  be  made  to  the  conditions  in  the  world  outside  which  are  reported 
to  the  brain.  Thus  all  the  sense  centers  form  intricate  connections  with  motor 
centers  for  the  production  of  motor  actions.  The  spinal  cord  and  part  of  the 
medulla  are  pathways  for  sensations  from  the  body  below  the  head  to  reach 
the  brain  and  for  motor  impulses  to  reach  the  body  muscles.  They  also  carry 
out  many  reflex  actions,  i.e.,  actions  resulting  from  direct  connections  of  sensory 
impulses  with  motor  responses  without  the  aid  of  the  brain.  The  medulla  is 
further  an  important  center  of  visceral  functions,  such  as  respiration,  heart- 
beat, etc. 

A  still  further  mechanism  is,  however,  required.  This  is  a  mechanism  for 
the  association  and  correlation  of  sensory  information  and  for  deciding  between 
simultaneous  ones.  Thus  suppose  an  animal  smells  some  food  and  sees  an  enemy 
simultaneously.  It  must  make  a  choice  between  the  motor  reactions  which 
would  result  from  each  of  these  sensations  if  they  were  received  separately.  It 
must  act  "intelligently"  in  such  situations.  Such  centers  of  correlation  are 
naturally  poorly  developed  in  simple  animals  and  become  more  and  more  promi- 
nent in  the  brain  as  the  complexity  of  the  animal  increases.  In  the  frog  correla- 
tion is  affected  mainly  in  the  optic  lobes  and  diencephalon  and  to  a  slight  extent 
in  the  cerebral  hemispheres.  Hence  the  complete  removal  of  the  cerebral 
hemispheres  in  the  frog  is  of  little  consequence  to  the  animal,  except  that  the 
sense  of  smell  is  lost  (see  Holmes,  p.  309).  In  higher  vertebrates  the  cerebral 
hemispheres  become  more  and  more  important  as  the  seat  of  correlation, 
co-ordination,  and  intelligent  action. 

The  cerebellum  is  also  a  co-ordination  center,  but  one  not  associated  with 
consciousness.  It  co-ordinates,  reinforces,  and  exercises  general  control  over 
motor  movements,  including  the  maintenance  of  equilibrium. 


THE  SPECIAL  ANATOMY  OF  THE  FROG  51 

H.      THE    SKELETON 

For  this  work  dried  mounted  skeletons  will  be  provided.  (The  student  may 
prepare  a  skeleton  as  follows:  Remove  all  possible  flesh  and  organs  from  a 
freshly  killed  frog,  and  dip  what  remains  from  time  to  time  in  hot  water,  brush- 
ing away  the  remaining  flesh  until  the  bones  are  cleaned.  Too  liberal  use  of  hot 
water  or  boiling  will  cause  the  bones  to  fall  apart.) 

1.  General  considerations  on  the  skeleton. — The  skeleton,  or  hard  parts 
of  the  body,  is  generally  of  two  kinds:  the  external  skeleton,  or  exoskeleton,  and 
the  internal  skeleton,  or  endoskeleton.     The  exoskeleton  covers  and  protects 
the  body  and  is  derived  from  the  skin.     Examples  are  scales,  feathers,  hair.     The 
frog  has  no  exoskeleton  except  such  as  has  become  fused  to  the  endoskeleton 
(see  below).     The  endoskeleton  is  the  internal  framework  of  the  body,  and  is 
composed  of  cartilage  in  the  embryo  which  becomes  partially  converted  into 
bone  in  the  adult  frog.     Such  bone  formed  in  cartilage  is  known  as  cartilage 
bone.     Investigation  shows  that  not  all  the  bones  of  the  frog's  skeleton  have 
arisen  in  this  way  but  some  have  appeared  in  connective  tissue  without  passing 
through  a  cartilage  stage.     Such  bones  are  called  membrane  bones,  dermal  bones, 
or  investing  bones.     They  are  produced  from  the  dermis  of  the  skin,  and  are  there- 
fore not  really  endoskeleton,  but  part  of  the  exoskeleton.     In  the  course  of 
evolution  these  bones,  originally  scales,  sank  into  the  body  and  attached  them- 
selves so  closely  to  the  endoskeleton  that  they  are  usually  treated  in  textbooks 
as  parts  of  the  endoskeleton.     The  clavicle  and  the  superficial  bones  of  the  skull 
and  jaws  of  the  frog  are  membrane  bones;   all  other  bones  of  the  skeleton  are 
cartilage  bones. 

The  skeleton  may  be  divided  into  an  axial  part  including  the  skull,  the 
visceral  skeleton,  and  the  vertebral  column;  and  an  appendicular  part  consisting 
of  the  bones  of  the  limbs,  the  girdles,  and  the  sternum  or  breastbone  (Holmes, 
chap,  xiii,  pp.  229-45). 

2.  The  vertebral  column  (Holmes,  pp.  237-38). — The  anterior  half  of  the 
vertebral  column  of  the  frog  consists  of  nine  bony  rings,  the  vertebrae;    the 
posterior  half  is  an  elongated  slender  bone,  the  urostyle.     Obtain  some  isolated 
vertebrae  and  identify  the  following  parts: 

a)  The  neural  canal  is  the  cavity  in  the  vertebra. 

b)  The  centrum  or  body  is  the  thickened  part  of  the  vertebra  ventral  to  the 
neural  canal.     It  articulates  with  the  centra  before  and  behind  it  by  a  ball  and 
socket  arrangement. 

c)  The  neural  arch  is  that  portion  which  arches  dorsally  over  the  neural  canal. 
<f)  The  neural  spine  is  a  sharp  dorsal  projection  from  the  center  of  the  neural 

arch. 

e)  The  transverse  processes  are  the  conspicuous  lateral  projections  extending 
horizontally  outward  from  the  place  of  junction  of  centrum  and  neural  arch. 


52  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

/)  The  zygapophyses  are  anterior  and  posterior  projections  from  the  neural 
arch,  one  in  front  of  and  one  behind  the  place  of  origin  of  each  transverse  process. 
They  link  successive  vertebrae  together. 

The  first  vertebra,  or  atlas,  differs  from  the  others  in  the  absence  of  the  trans- 
verse processes  and  the  presence  of  special  articulating  surfaces  for  holding  the 
skull.  Between  the  atlas  and  the  skull  is  a  gap  which  permits  the  operation  of 
pithing.  The  transverse  processes  of  the  last  vertebra  articulate  with  the  pelvic 
girdle,  and  this  vertebra  is  hence  called  the  sacral  vertebra. 

3.  The  skull  and  the  visceral  skeleton. — The  visceral  skeleton  includes  the 
upper  and  lower  jaws,  the  hyoid  apparatus,  and  the  cartilages  of  the  larynx. 
It  is  so  called  because  originally  all  of  these  structures  were  paired  semicircular 
cartilages,  used  to  support  the  gills.  Since  gills  are  part  of  the  walls  of  the 
alimentary  canal,  the  appropriateness  of  the  term  "visceral  skeleton"  becomes 
apparent.  Six  such  cartilaginous  hoops  are  present  in  the  frog  tadpole,  of  which 
the  first  becomes  in  the  adult  frog  the  basis  of  upper  and  lower  jaws,  while  the 
remaining  ones  undergo  remarkable  transformations  into  the  hyoid  and  laryngeal 
cartilages.  The  laryngeal  cartilages  will  not  be  studied. 

The  original  cartilage  skull,  forming  a  case  to  inclose  the  brain,  fused  in  front 
with  the  olfactory  capsules  containing  the  organ  of  smell,  behind  with  the  otic 
capsules  containing  the  ears,  and  below  with  the  cartilaginous  bars  which  formed 
the  upper  jaw  while  the  similar  bars  of  the  lower  jaw  remained  separate  and 
formed  a  joint  with  the  skull.  Part  of  the  cartilage  of  these  structures  persists 
in  the  adult  skull,  part  is  converted  into  cartilage  bones,  and  both  of  these  are 
partly  concealed  by  a  superficial  covering  of  membrane  bones. 

a)  Dorsal  aspect  of  the  skull  and  upper  jaw  (Holmes,  chap,  xiii,  pp.  229-37). — 
Examine  the  dried  skull  and  note  that  the  membrane  bones  can  be  distinguished 
easily  from  the  cartilage  bones  by  their  lighter  color,  smoother  surfaces,  thin 
and  flat  shapes,  and  more  superficial  position.  The  cartilage  has  of  course  dis- 
appeared in  a  dried  skull.  The  skull  proper  forms  the  central  region,  while  the 
lower  jaw,  which  is  fused  to  the  skull,  appears  as  an  arch  on  each  side  and  in 
front  of  the  skull.  A  large  gap,  the  orbit,  which  holds  the  eye,  is  thus  left  between 
skull  and  jaw. 

The  bones  of  the  dorsal  side  of  the  skull  proper  are: 

(1)  Nasal  bones,  two  triangular  membrane  bones  just  behind  the  external 
nares. 

(2)  Sphenethmoid  bone,  a  single  ring-shaped  cartilage  bone  in  the  median 
line  behind  the  nasals. 

(3)  Frontoparietal  bones,  two  long  flat  membrane  bones  posterior  to  the 
sphenethmoid.     In  other  animals  the  anterior  frontal  portion  is  separate  from 
the  posterior  parietal  portion  of  this  bone. 

(4)  Exoccipital  bones,  the  two  cartilage  bones  forming  the  posterior  extremity 
of  the  skull.     They  surround  a  large  opening,  the  foramen  magnum,  through 


THE  SPECIAL  ANATOMY  OF  THE  FROG  53 

which  the  medulla  oblongata  passes  to  become  continuous  with  the  spinal  cord. 
Ventrally  they  bear  two  rounded  prominences,  the  occipital  condyles,  by  which 
the  skull  articulates  with  the  atlas. 

(5)  Pro-otic  bones,  the  cartilage  bones  extending  laterally  from  the  posterior 
end  of  the  frontoparietals.  They  are  ossified  in  the  otic  capsule  and  hence  inclose 
the  ear. 

The  bones  of  the  upper  jaw  or  maxillary  arch  are : 

(1)  Premaxilla,  a  pair  of  small  membrane  bones  in  front  of  the  external 
nares. 

(2)  Maxilla,  the  long  slender  membrane  bone  forming  the  greater  part  of  the 
sides  of  the  jaw.     Premaxillae  and  maxillae  bear  teeth. 

(3)  Quadratojugal,  the  short  slender  membrane  bone  behind  the  maxilla,  not 
bearing  teeth. 

(4)  Squamosal,  the  curious  T-shaped  membrane  bone  extending  from  the 
posterior  end  of  the  quadratojugal  to  the  pro-otic. 

(5)  Pterygoid,  a  three-rayed  cartilage  bone  under  the  squamosal  but  visible 
from  the  dorsal  side. 

(6)  The  quadrate  cartilage  lies  between  the  squamosal  and  the  pterygoid  and 
is  the  place  of  attachment  of  the  lower  jaw  to  the  skull. 

b)  Ventral  aspect  of  the  skull.     The  ventral  bones  of  the  skull  are: 

(1)  Vomer,  a  pair  of  membrane  bones  behind  the  premaxillae,  forming  the 
floor  of  the  olfactory  capsules  and  bearing  teeth. 

(2)  Palatine,   two   slender  cartilage  bones  extending  laterally  from  just 
behind  the  vomerine  teeth  to  the  maxillae. 

(3)  Parasphenoid,  a  single  long  dagger-shaped  membrane  bone  on  the  ventral 
surface  of  the  skull,  its  lateral  posterior  processes  underlying  the  auditory 
capsules.     The  point  of  the  dagger  underlies  the  ventral  side  of  the  sphenethmoid 
ring. 

c)  The  bones  of  the  lower  jaw  or  mandibular  arch.    These  are: 

(1)  Mentomeckelian  bones,  two  small  cartilage  bones  at  the  tip  of  the  lower 
jaw.    They  are  ossified  in  the  original  cartilage  bars  (MeckePs  cartilage)  which 
were  the  lower  jaw  of  the  tadpole. 

(2)  Dentary,  a  short  membrane  bone  behind  the  preceding  on  the  outer  surface 
of  the  jaw. 

(3)  Angulosplenial,  the  long  slender  membrane  bone  forming  the  greater 
part  of  the  jaw.     Its  anterior  end  is  under  the  dentary.     Its  outer  surface  behind 
the  dentary  is  grooved.     In  this  groove  is  located  in  life  MeckePs  cartilage,  which 
articulates  with  the  quadrate  cartilages  of  the  skull. 

d)  Hyoid  apparatus.     This  portion  of  the  skeleton  is  usually  lacking  in  dried 
material.     Most  of  its  parts  have  already  been  seen  during  the  dissection  of  the 
frog  and  should  be  examined  again  and  further  exposed  in  your  preserved  speci- 
men (Holmes,  p.  324). 


54  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

(1)  The  body  of  the  hyoid  is  the  flat  plate  of  cartilage  in  the  floor  of  the  buccal 
cavity.     Its  concave  anterior  margin  receives  the  base  of  the  tongue.     Its 
lateral  anterior  corners  have  short  alary  processes,  and  its  posterior  corners 
poster o-lateral  processes. 

(2)  The  anterior  horns  or  cornua  of  the  hyoid  are  the  long,  slender  rods  which 
curve  back  from  the  anterior  margin  of  the  body  to  the  pro-otic  bones  of  the 
skull. 

(3)  The  thyroid  processes  or  posterior  horns  are  the  two  processes  which 
diverge  from  the  posterior  margin  inclosing  the  laryngeal  chamber  between  them. 
They  are  ossified  while  the  other  parts  of  the  hyoid  are  cartilaginous. 

(4)  The  columella,  the  small  slender  bone  in  the  middle  ear,  one  end  of  which 
is  attached  near  the  middle  of  the  tympanic  membrane,  is  probably  a  part  of  the 
hyoid  apparatus. 

4.  Bones  of  the  pectoral  girdle  (Holmes,  p.  238). — The  pectoral  girdle  forms 
a  bony  arch  for  the  support  of  the  fore  limbs.     It  is  incomplete  dorsally  and  has 
no  connection  with  the  vertebral  column.     Ventrally  its  two  halves  are  united 
by  the  interposition  of  the  sternum.     Each  half  of  the  girdle  consists  of: 

a)  Suprascapula,  the  most  dorsal  bone,  large  and  flat  with  a  cartilage  along 
its  free  dorsal  border. 

b)  Scapula,  the  bone  ventral  to  the  preceding  and  containing  a  cup-shaped 
cavity,  the  glenoid  fossa,  in  which  the  long  bone  of  the  upper  arm  is  inserted. 

c)  Clavicle,  the  anterior  bone  of  the  two  which  compose  the  ventral  aspect 
of  the  girdle.     It  is  a  membrane  bone,  the  only  one  in  the  skeleton  outside  of  the 
skull  and  jaws. 

d)  Procoracoid,  the  cartilage  which  is  covered  over  by  the  clavicle  and  which 
fails  to  ossify  because  its  function  is  usurped  by  the  clavicle. 

e)  Coracoid,  the  posterior  of  the  two  ventral  bones.     It  takes  part  in  the 
glenoid  fossa. 

5.  The  sternum  (Holmes,  p.  240). — The  sternum  is  a  chain  of  bones  and 
cartilages  between  the  two  ventral  ends  of  the  halves  of  the  pectoral  girdle. 

a)  Episternum,  the  rounded  catilage  forming  the  anterior  extremity  of  the 
sternum. 

b)  Omosternum,  the  bone  behind  the  preceding. 

c)  Epicoracoids,  the  cartilages  between  the  medial  ends  of  the  coracoid  bones. 

d)  Sternum  proper  or  mesosternum,  bony  rod  behind  the  coracoids. 

e)  Xiphisternum,  terminal  rounded  cartilage. 

6.  Bones  of  the  pelvic  girdle  (Holmes,  pp.  242-43). — This  is  the  bony  girdle 
which  supports  the  hind  limbs.     It  is  complete  dorsally,  forming  a  joint  with  the 
transverse  processes  of  the  last  vertebra.     The  bones  of  each  half  of  the  pelvic 
girdle  are: 

a)  Ilium,  the  long  scythe-shaped  dorsal  bone  which  extends  forward  parallel 
to  the  urostyle  to  articulate  with  the  transverse  processes  of  the  sacral  vertebra. 


THE  SPECIAL  ANATOMY  OF  THE  FROG  55 

b)  Pubis,   the  anterior  portion  of   the  semicircular   crest  which  projects 
ventrally  from  that  part  of  the  pelvic  girdle  which  lies  medially  between  the 
heads  of  the  two  long  thigh  bones. 

c)  Ischium,  the  posterior  portion  of  the  crest. 

The  two  pubes  and  the  two  ischia  are  completely  fused  in  the  median  ventral 
line  producing  the  projecting  crest  mentioned  above.  These  unions  are  named 
the  pubic  and  ischial  symphyses.  For  the  exact  boundaries  between  the  three 
bones  of  the  girdle  see  Holmes,  Fig.  69,  p.  242.  The  cuplike  cavity  on  each  side 
of  the  girdle  which  receives  the  head  of  the  thigh  bone  is  called  the  acetabulum. 

7.  Bones  of  the  limbs. — The  skeleton  of  the  fore  and  hind  limbs  is  evidently 
built  upon  the  same  plan,  and  the  bones  evidently  correspond.  The  two  limbs 
will  therefore  be  considered  together  (Holmes,  pp.  241,  243,  and  Fig.  63,  p.  230). 

a)  The  upper  part  of  each  limb  consists  of  a  long  bone.     In  the  fore  limb 
this  is  the  humerus;  in  the  hind  limb,  the  femur.     The  humerus  bears  a  conspicu- 
ous crest,  the  deltoid  ridge,  so  named  because  the  deltoid  muscle  is  inserted  there. 

b)  The  next  section  of  the  limb  is  generally  composed  of  two  bones,  but  in 
the  frog  these  two  are  in  the  case  of  both  limbs  fused  into  one.     This  is  the  radio- 
ulna  in  the  fore  limb,  tibio-fibula  in  the  hind  limb.     A  longitudinal  groove  along 
the  center  of  both  surfaces  of  each  of  these  bones  indicates  the  place  of  fusion  of 
the  two  originally  separate  components,  the  radius  and  ulna  in  the  forearm,  the 
tibia  and  fibula  in  the  shank.     Radius  and  tibia  correspond  and  are  on  the  thumb 
side  (preaxial  side)  of  the  limb;    ulna  and  fibula  are  on  the  little  finger  side 
(postaxial). 

c)  Wrist  and  ankle  constitute  the  next  section  of  the  limbs.    The  wrist  or 
carpus  consists  of  six  small  bones  in  two  rows.     These  are  generally  difficult  to 
make  out  in  ordinary  preparations  of  the  skeleton.     The  ankle  or  tarsus  is 
unusually  elongated  in  the  frog  and  consists  chiefly  of  two  relatively  large  bones, 
the  astragalus  on  the  preaxial  side  and  the  calcaneum  on  the  postaxial  side. 
Between  these  and  the  foot,  two  or  three  minute  bones  occur. 

d)  The  palm  of  the  hand  and  sole  of  the  foot  each  consist  of  five  slender 
diverging  bones,  the  metacarpals  and  metatarsals,  respectively.     The  first  meta- 
carpal  is  rudimentary. 

e)  The  fingers  and  toes  are  supported  by  small  bones,  called  phalanges. 


I.      THE  MUSCULAR  SYSTEM 

The  frog  has  two  types  of  muscles,  the  involuntary  muscles  found  in  the 
viscera,  and  the  voluntary  ones  attached  either  directly  or  indirectly  to  the 
skeleton.  The  arrangement  of  the  muscles  of  the  viscera  has  already  been  seen 
in  the  study  of  the  microscopic  structure  of  the  organs.  They  are  commonly 
arranged  in  cylindrical  tubes,  in  which  the  fibers  run  in  either  a  circular  or  a 
longitudinal  direction.  The  voluntary  muscles,  on  the  other  hand,  have  no 


56  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

such  simple  arrangement,  and  a  study  of  each  one  is  necessary  to  understand 
its  action.  The  term  "muscular  system"  generally  refers  to  the  voluntary 
muscles. 

For  the  study  of  the  muscles  frogs  which  have  been  preserved  for  some 
time  in  formalin  should  be  employed.  Those  in  which  the  viscera  have  been 
dissected  are  usable  for  this  purpose.  Remove  the  skin  completely. 

1.  Parts  and  relations  of  a  muscle. — Examine  the  large  gastrocnemius  muscle 
on  the  back  of  the  shank  as  an  illustration  of  a  typical  muscle.     Identify  its 
parts  as  follows: 

a)  The  fascia  is  the  shining  tough  connective  tissue  membrane  which  incloses 
the   muscle. 

b)  The  tendon  is  the  shining  tough  band  or  cord  at  each  end  of  the  muscle. 
It  is  produced  by  the  extension  and  concentration  of  the  fascia  beyond  the 
fleshy  part.     By  means  of  tendons,  muscles  are  firmly  attached  to  bones,  other 
tendons,  or  other  fixed  structures.     Tendons  may  be  of  many  shapes,  depending 
upon  the  shape  of  the  muscle  of  which  they  are  a  part. 

c)  The  belly  is  the  fleshy  part  of  the  muscle. 

d)  The  origin  is  the  more  fixed  point  of  attachment  of  the  muscle,  i.e.,  the 
part  which  does  not  move  when  the  muscle  contracts.     The  gastrocnemius  has 
two  points  of  origin,  or  heads,  as  they  are  often  called,  at  the  upper  end  of  its 
(apparently)  dorsal  surface.     The  larger  of  these  attaches  the  main  mass  of  the 
muscle  to  a  tendon  which  passes  from  the  distal  end  of  the  femur  to  the  upper 
end  of  the  tibio-fibula;   the  smaller  is  a  slender  tendon  which  joins  the  general 
tendon  passing  over  the  knee.     With  a  forceps  loosen  the  other  muscles  from 
about  the  heads  of  the  gastrocnemius  and  verify  these  points. 

e)  The  insertion  is  the  more  movable  point  of  attachment  of  the  muscle, 
i.e.,  the  part  which  is  moved  by  the  action  of  the  muscle.     The  lower  end  of 
the  gastrocnemius  tapers  to  a  strong  tendon  (the  famous  tendon  of  Achilles), 
which  passes  over  and  is  attached  to  the  ankle  bones  and  then  becomes  continuous 
with  the  broad  plantar  fascia  which  covers  the  sole  of  the  foot. 

/)  The  action  of  a  muscle  is  a  description  of  its  function.  The  gastrocnemius 
through  its  insertion  on  the  ankle  can  bend  the  entire  leg  below  the  knee  up 
against  the  thigh  (flexion  of  the  leg) ;  through  its  continuity  with  the  plantar 
fascia  it  can  straighten  the  foot  (extension  of  the  foot).  Test  these  actions  by 
pulling  on  the  gastrocnemius. 

2.  General  account  of  the  muscles  of  the  frog  (Holmes,  chap,  xiv,  pp.  246- 
57). — We  shall  undertake  to  study  only  the  superficial  and  easily  identifiable 
muscles,  particularly  those  which  are  of  interest  in  the  physiology  of  the  frog. 
Most  of  the  following  muscles  have  the  same  names,  positions,  and  action  as 
in  man  and  other  vertebrates,  and  the  statements  about  them  are  hence  of  general 
application.    No  attempt  is  made  to  give  all  the  details  of  the  origin  and  insertion . 


THE  SPECIAL  ANATOMY  OF  THE  FROG  57 

In  studying  muscles  separate  each  one  from  its  fellows  as  carefully  as  possible 
with  a  forceps  or  probe,  and  determine  the  origin,  insertion,  and  general  action 
of  each. 

a)  Muscles  of  the  lower  jaw:  Pull  off  all  tissue  between  the  eye  and  tympanic 
membrane.     Pull  off  the  tympanic  membrane,  identifying  underneath  it  a  circu- 
lar cartilage,  the  tympanic  ring,  resting  upon  the  squamosal  bone.     Between 
the  tympanic  ring  and  the  eye  a  mass  of  muscles  will  be  found  passing  to  the 
lower  jaw,  on  the  inner  side  of  the  posterior  end  of  the  upper  jaw.     Remove  the 
end  of  the  upper  jaw  (quadratojugal  bone)  so  as  to  reveal  the  complete  course 
of  these  muscles.     The  following  three  may  be  readily  identified: 

(1)  The  temporal  muscle  arises  from  the  side  of  the  skull  and  passes  down 
between  the  eye  and  the  tympanic  ring  to  be  inserted  on  the  posterior  end  of  the 
lower  jaw.     Action,  closes  the  mouth  (elevator  of  the  jaw). 

(2)  The  masseters  originate  from  the  tympanic  ring  and  adjacent  bones  and 
are  inserted  on  the  lower  jaw  behind  the  temporal.    Action,  same  as  preceding; 
also  stretch  the  tympanic  membrane. 

(3)  The  depressor  mandibuli  is  a  muscle  of  the  jaw  located  behind  the 
tympanic  ring.     It  arises  from  the  tympanic  ring  and  from  the  general  fascia 
of  the  back  (dorsal  fascia)  and  passes  to  the  extreme  posterior  tip  of  the  lower 
jaw,  where  it  is  fastened  to  Meckel's  cartilage.     Action,  opens  the  mouth 
(depressor  of  the  jaw)  and  stretches  the  tympanic  membrane.     Pull  the  lower  jaw 
fully  open  to  see  more  clearly  the  arrangement  of  these  three  muscles. 

b)  Muscles  of  the  dorsal  side  of  the  trunk:  This  portion  of  the  body  is  more 
or  less  covered  by  the  dorsal  fascia,  a  strong  membrane  fastened  to  the  ilium 
bones,  the  neural  arches  of  the  vertebrae,  and  the  skull,  and  furnishing  a  place 
of  insertion  of  many  muscles.     Easily  identifiable  muscles  of  the  back  beginning 
behind  the  ear  are: 

(1)  The  dorsalis  scapulae  is  the  anterior  half  of  the  large  triangular  mass 
behind  and  partially  covered  by  the  depressor  mandibuli.     Origin,  from  the 
dorsal  margin  of  the  suprascapula;  remaining  course  like  the  next. 

(2)  The  latissimus  dorsi  is  the  posterior  portion  of  the  triangular  mass. 
Origin,  dorsal  fascia;   unites  with  the  preceding  to  be  inserted  on  the  deltoid 
ridge  of  the  humerus;  action,  raises  the  fore  limb  upward  and  backward  (abduc- 
tion of  the  limb). 

(3)  The  longissimus  dorsi  is  the  long  muscle  extending  from  the  anterior 
third  of  the  urostyle  forward  to  the  skull.     Remove  the  dorsal  fascia  and  pre- 
ceding muscles  to  see  its  full  course.     It  is  attached  at  many  places  to  the 
vertebrae.    Action,  raises  the  head  and  straightens  the  back. 

(4)  The  coccygeo-sacralis  runs  diagonally  from  the  urostyle  just  behind  the 
insertion  of  the  preceding  muscle  to  the  transverse  process  of  the  sacral  vertebra. 
Pull  off  the  remainder  of  the  dorsal  fascia  to  see  it.    Action,  draws  the  back 


58  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

nearer  the  urostyle  or  vice  versa  when  both  muscles  of  the  two  sides  act  together, 
or  turns  the  back  to  one  side,  when  acting  singly. 

(5)  The  coccygeo-iliacus  is  the  diagonal  muscle  parallel  to  and  behind  the 
preceding  running  from  the  posterior  two-thirds  of  the  urostyle  to  the  ilium. 
Action,  fixes  the  urostyle  with  respect  to  the  pelvic  girdle. 

c)  Muscles  of  the  sides  of  the  abdomen: 

(1)  The  external  oblique  is  the  large  muscle  covering  the  sides  of  the  abdomen 
extending  from  the  dorsal  fascia  and  the  ilium  to  the  linea  alba.     Its  fibers  run 
diagonally  backward.     Action,  to  support  and  reduce  the  abdominal  cavity,  and 
to  cause  exhalation  in  lung  breathing. 

(2)  The  transverse  (including  the  internal  oblique  of  other  vertebrates)  lies 
under  the  preceding,  its  fibers  running  diagonally  forward.     Strip  off  the  external 
oblique  cautiously  to  see  it.     Relations  and  function  similar  to  preceding. 

d)  Muscles  of  the  ventral  side  of  the  trunk: 

(1)  The  rectus  abdominis  is  the  flat  segmented  muscle  lying  on  both  sides 
of  the  median  ventral  line,  extending  from  the  pubic  symphysis  to  the  sternum. 
Action,  supports  the  abdominal  contents,  and  fixes  the  sternum  in  place. 

(2)  The  pectoral  muscle  is  the  large  muscle  of  the  anterior  ventral  part  of  the 
body.     It  arises  from  the  various  parts  of  the  sternum  and  from  the  lateral 
border  of  the  fascia  of  the  rectus  abdominis  muscle.     It  is  inserted  on  the  deltoid 
ridge  of  the  humerus.     Action,  draws  the  arm  toward  the  ventral  side  and  leg 
(adductor  of  the  arm)  and  expands  the  abdominal  cavity. 

e)  Muscles  of  the  floor  of  the  mouth  and  the  hyoid  apparatus: 

(1)  The  mylohyoid  is  a  thin  sheet  of  muscle  running  crosswise  from  one  half 
of  the  lower  jaw  to  the  other  along  their  whole  extent.     It  forms  the  outermost 
layer  of  the  buccal  floor  and  its  function  is  to  raise  this  floor  in  the  breathing 
movements. 

(2)  The  submental  muscle.     Cut  through  the  mylohyoid  muscle  in  its  median 
ventral  line  and  deflect  the  two  halves.     Under  it  at  the  very  anterior  tip  of  the 
lower  jaw  is  the  small  submental  muscle.     Its  contraction  pushes  the  sublingual 
tubercle  upward  against  the  premaxillary  bones  of  the  upper  jaw  and  thereby 
closes  the  external  nares  in  lung  respiration. 

(3)  The  geniohyoid  muscle  comprises  the  longitudinal  bands  revealed  by  the 
removal  of  the  mylohyoid,  consisting  of  medial  and  lateral  portions  arising 
under  the  submental  muscle  and  lateral  to  it  from  the  lower  jaw,  and  extending 
to  the  postero-lateral  processes  of  hyoid  and  the  body  of  the  hyoid  as  far  as  the 
forking  of  the  thyroid  processes.     Action,  pulls  the  hyoid  apparatus  powerfully 
forward,  thus  raising  the  floor  of  the  buccal  cavity  in  respiration;    also  helps 
to  swallow,  to  open  the  mouth,  to  lower  the  tip  of  the  jaw,  thus  opening  the 
nares,  and  to  move  the  tongue. 

(4)  The  sternohyoid  is  a  continuation  forward  of  the  rectus  abdominis, 
extending  from  the  underside  of  the  coracoid  and  clavicle  to  the  body  of  the 


THE  SPECIAL  ANATOMY  OF  THE  FROG  59 

hyoid.  It  is  readily  seen  when  the  pectoral  girdle  is  lifted  up.  It  and  a  small 
muscle  lateral  to  it  (omohyoid)  exert  a  pull  upon  the  body  of  the  hyoid,  causing 
it  to  bulge  outward,  and  hence  lower  the  floor  of  the  buccal  cavity  in  breathing. 
Their  action  is  thus  the  opposite  of  that  of  the  preceding  muscles. 

(5)  The  petrohyoids  are  several  small  muscles  under  the  sterno-  and  omo- 
hyoids  extending  from  the  otic  capsule  to  the  sides  of  the  hyoid  apparatus. 
They  raise  the  hyoid  apparatus  and  hence  the  floor  of  the  buccal  cavity  in 
respiration,  acting  in  antagonism  to  the  preceding  muscle,  and  by  their  com- 
pressing effect  upon  the  larynx  and  pharynx  are  of  great  importance  in  swallowing 
food  and  air. 

/)  Muscles  of  the  tongue: 

(1)  The  hyoglossus  is  the  conspicuous  muscle  in  the  median  ventral  line  of 
the  throat  under  the  geniohyoid.     Each  half  of  it  originates  at  the  posterior 
end  of  the  thyroid  process  of  the  hyoid,  extends  forward  covering  this  process, 
meets  its  fellow  where  the  processes  spring  from  the  body  of  the  hyoid.     The 
muscle  thus  formed  runs  forward  in  contact  with  the  body  of  the  hyoid  up  to  the 
base  of  the  tongue  into  which  it  disappears.     It  is  the  retractor  of  the  tongue 
(draws  it  back  into  the  mouth  after  use). 

(2)  The  genioglossus  is  a  small  but  thick  muscle  lying  in  front  of  the  anterior 
end  of  the  hyoglossus  and  originating  from  the  lower  jaw  under  the  submental 
muscle.     It  is  the  protractor  of  the  tongue  (throws  it  forward). 

g)  Muscles  of  the  thigh:  The  thigh  presents  apparent  dorsal  and  ventral  sides 
and  anterior  and  posterior  surfaces.  These  are  not  really  such  because  the  leg 
of  the  frog  has  been  twisted  from  the  primitive  vertebrate  position.  The 
ventral  surface  is  really  anterior  and  hence  more  correctly  called  preaxial;  and  the 
dorsal  surface  is  posterior  or  postaxial.  Anterior  was  originally  dorsal  and  pos- 
terior ventral.  However,  in  order  to  simplify  the  following  description,  the  same 
names  will  be  applied  as  for  other  parts  of  the  body,  according  to  the  apparent 
positions.  Separate  all  of  the  muscles  of  the  thigh  from  each  other  before 
proceeding. 

(1)  The  triceps  femoris  is  the  great  muscle  which  covers  the  whole  anterior 
part  of  the  thigh,  its  powerful  tendon  passing  over  the  knee  to  the  tibio-fibula. 
It  has  three  origins  or  heads  and  consists  of  three  parts.     The  ventral  part 
(vastus  internus  or  crural]  arises  from  the  borders  of  the  acetabulum.     The  small 
middle  portion  (tensor  fasciae  latae)  originates  on  the  ilium  and  ends  in  the 
fascia  (fascia  lata),  which  covers  the  triceps  femoris.     The  dorsal  part  is  the 
vastus  externus  or  glutens  magnus  and  arises  from  the  side  of  the  posterior  end 
of  the  crest  of  the  ilium.     The  triceps  femoris  is  the  great  extensor  of  the  shank, 
and  also  may  draw  the  leg  up  against  the  body  (abduction). 

(2)  The  iliacus  muscles  are  those  which  extend  from  a  considerable  part  of 
the  crest  of  the  ilium  between  the  tensor  fasciae  latae  and  the  vastus  externus 
to  the  femur.     They  are  abductors  of  the  leg. 


60  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

(3)  The  ileo-fibularis  is  the  slender  muscle  next  to  the  vastus  externus  on 
the  dorsal  side  of  the  thigh.     It  extends  from  the  ilium  to  the  upper  end  of  the 
tibio-fibula,  draws  the  thigh  dorsaily,  and  flexes  the  shank. 

(4)  The  semimembranosus  is  the  posterior  muscle  of  the  dorsal  side  of  the 
thigh.     It  arises  from  the  ischial  symphysis,  is  inserted  on  the  tibio-fibula,  bends 
the  shank,  and  draws  the  leg  toward  the  median  line  (adduction). 

(5)  The  gracilis  major  and  minor  (rectus  internus  major  and  minor  in  Holmes, 
Fig.  70,  p.  249)  are  the  posterior  muscles  of  the  ventral  side  of  the  thigh  on  the 
other  side  of  the  leg  from  the  preceding.     The  minor  is  small  and  the  most 
posterior  one.     Both  extend  from  the  ischium  to  the  knee  and  have  the  same 
action  as  the  preceding  muscle. 

(6)  The  adductor  magnus  is  the  muscle  next  anterior  to  the  gracilis  major 
on  the  ventral  side.     Most  of  it  is  concealed  by  gracilis  major  and  the  muscle 
to  be  mentioned  next.     It  originates  on  the  ischial  and  pubic  symphyses  and  is 
inserted  on  the  femur.     It  adducts  the  thigh  and  leg. 

(7)  The  sartorius  is  the  flat  thin  muscle  crossing  the  lower  end  of  the  adductor 
magnus.     It  arises  on  the  pubic  symphysis  and  joins  the  general  tendon  over  the 
knee.    Action,  bends  the  shank  and  aducts  the  thigh. 

(8)  The  adductor  longus  is  a  thin  flat  muscle  under  the  sartorius  but  generally 
peeping  out  along  the  latter's  anterior  border.     It  originates  on  the  ilium,  joins 
and  acts  with  the  adductor  magnus. 

(9)  The  semitendinosus  is  a  muscle  of  peculiar  shape  under  the  gracilis  major, 
which  should  be  removed  to  see  it.     It  has  two  separate  tendinous  heads  from 
the  ischium  and  two  separate  bellies,  uniting  to  one  tendon  fastened  to  the 
upper  end  of  the  tibio-fibula.     It  acts  like  the  gracilis  major. 

ti)  Muscles  of  the  shank: 

(1)  The  gastrocnemius  has  been  sufficiently  described. 

(2)  The  peroneus  is  the  only  other  muscle  on  the  dorsal  aspect  of  the  shank. 
It  extends  from  the  general  tendon  over  the  knee  to  the  lower  end  of  the  tibio- 
fibula  and  the  ankle.     It  extends  and  twists  the  foot  and  brings  the  shank  up 
against  the  thigh,  as  in  swimming  and  leaping  movements. 

(3)  The  tibialis  muscles  are  the  small  muscles  of  the  shank  lying  next  to  the 
bone.     There  are  three  of  them.     The  tibialis  anticus  longus  covers  the  anterior 
surface  of  the  tibio-fibula;  it  arises  by  a  slender  tendon  from  the  lower  end  of  the 
femur  and  soon  divides  into  two  bellies,  which  are  attached  by  slender  tendons 
to  the  ankle  bones.     Action,  bends  the  ankle.     Beneath  the  lower  part  of  this 
muscle  is  the  small  tibialis  anticus  brevis,  originating  on  the  middle  of  the  tibio- 
fibula,  and  inserted  on  the  ankle,  which  it  also  flexes.     The  tibialis  posticus  is  a 
long  slim  muscle  on  the  ventral  aspect  of  the  shank,  between  the  gastrocnemius 
and  the  tibio-fibula,  to  which  it  is  attached  along  its  entire  length.     It  is  likewise 
inserted  on  the  ankle,  which  it  flexes  and  twists. 

(4)  The  extensor  cruris  is  a  small  muscle  on  the  anterior  aspect  of  the  shank, 
lying  next  to  the  upper  two-thirds  of  the  tibio-fibula  and  in  contact  dorsaily 


THE  SPECIAL  ANATOMY  OF  THE  FROG  61 

with  the  tibialis  anticus  longus.     It  originates  on  the  femur  and  straightens  the 
shank  in  the  leaping  and  swimming  movements. 

J.      GENERAL  ANATOMICAL  PRINCIPLES 

Now  that  we  have  completed  our  study  of  the  anatomy  of  the  frog, 
attention  may  be  called  to  some  of  the  general  principles  which  underlie  its 
construction. 

1.  Principle  of  bilateral  symmetry. — The  parts  of  the  frog  are  arranged  sym- 
metrically with  reference  to  a  median  vertical  plane  which  was  named  in  the 
early  part  of  this  outline  the  sagittal  plane.    These  parts  are  either  single 
(unpaired)  and  lie  in  the  sagittal  plane  which  divides  them  into  identical  right 
and  left  halves,  or  they  are  double  (paired)  and  placed  at  the  same  level  of  the 
body  at  equal  distances  from  the  sagittal  plane.     Unpaired  structures  are  the 
skull  and  vertebral  column,  brain  and  spinal  cord,  heart,  digestive  tract,  post- 
caval  vein,  and  dorsal  aorta.    All  the  muscles,  the  appendicular  skeleton,  the 
nerves  and  chief  sense  organs,  most  of  the  blood  vessels,  the  lungs,  kidneys, 
reproductive  organs  and  their  ducts  are  paired.     The  digestive  tract  is  the  chief 
unsymmetrical  system  in  the  body,  but  it  obviously  began  as  a  median  tube 
extending  from  mouth  to  anus  and  only  subsequently  developed  the  lateral 
displacements  and  spiral  ceilings  which  have  destroyed  its  symmetry. 

2.  Principle  of  segmentation. — Less  readily  recognizable  is  the  fact  that  the 
structure  of  the  frog  is  based  upon  a  repetition  of  parts  along  the  sagittal  axis. 
The  frog  is  thus  conceived  of  as  built  up  of  a  series  of  sections,  or  segments.    These 
segments  are  similar  to  each  other,  each  has  perfect  bilateral  symmetry  and 
contains  a  portion  of  each  of  the  systems  of  the  body.     In  the  adult  frog  seg- 
mentation is  best  illustrated  by  the  spinal  cord  and  its  nerves,  the  vertebral 
column,  and  some  parts  of  the  circulatory  system  (vessels  to  the  body  wall, 
kidneys,  and  reproductive  organs),  all  of  which  exhibit  obvious  repetition  along 
the  axis,  and  to  a  less  extent  in  the  muscles  (rectus  abdominis  and  longissimus 
dorsi  muscles).     The  segmentation  is  much  more  complete  in  the  tadpole. 

3.  Principle  of  cephalization.— Segmentation  is  retained  most  completely 
in  the  posterior  portion  of  the  body,  less  so  in  anterior  regions,  and  is  almost 
entirely  lost  in  the  head.     Investigation  shows,  however,  that  the  head  like  the 
rest  of  the  body  originally  consisted  of  a  series  of  segments,  and  traces  of  this 
segmentation  still  persist  in  the  lobed  condition  of  the  brain,  in  the  cranial  nerves, 
and  muscles  of  the  eye.     But  these  segments  for  the  most  part  fused  together 
in  order  to  produce  a  structure,  the  head,  which  should  be  more  specialized, 
more  efficient  than  the  other  parts  over  which  it  acquires  dominance,  just  as 
men  and  nations  combine  together   for   greater   efficiency  and  achievements. 
Correlated  with  this  dominance  of  the  head  and  anterior  regions  is  a  descent 
of  the  viscera  posteriorly.     Cephalization  is  the  name  which  is  applied  to  the 
development  and  specialization  of   the  head  at  the  expense  of  the  rest  of 
the  body. 


VI.    THE  PROCESS  OF  CELL  DIVISION 

All  cells  arise  from  pre-existing  cells  by  a  process  of  division.  In  a  few  cases 
this  is  a  simple  splitting,  or  direct  division,  but  in  the  vast  majority  of  cases  the 
cell  divides  by  a  complicated  process,  known  as  indirect  division,  mitosis,  or 
karyo kinesis.  In  mitosis,  both  the  nucleus  and  the  cytoplasm  are  involved  in  a 
complex  and  remarkable  behavior. 

The  following  materials  have  been  found  to  be  the  most  favorable  for  the 
study  of  mitosis:  the  developing  eggs  of  Ascaris,  a  parasitic  worm;  the  root  tips 
of  plants,  chiefly  the  onion,  the  hyacinth,  or  Tradescantia;  the  developing  eggs  of 
fish.  A  complete  outline  is  provided  below  for  the  study  of  mitosis  in  the  eggs 
of  Ascaris;  and  following  this  are  brief  statements  regarding  the  other  materials 
and  the  points  in  which  they  differ  from  Ascaris. 

A.      MITOSIS   IN   THE   EGGS   OF   Ascaris 

Ascaris  megalocephala,  commonly  used  for  this  purpose,  is  a  parasitic  round 
worm  found  in  the  intestine  of  the  horse.  (A  description  of  this  animal  is  given 
in  Hegner,  p.  160.)  The  fertilized  eggs  pass  down  the  long  oviducts  of  the 
worm,  dividing  as  they  go.  Obviously  by  cutting  longitudinal  slices  through 
the  oviducts  at  the  proper  levels,  eggs  in  all  stages  of  division  will  be  obtained. 
The  slides  bear  such  longitudinal  slices  of  the  oviduct. 

Examine  the  slide  "  A  scaris— mitosis"  with  the  low  power.  Identify  in  each 
long  slice  upon  the  slide  the  thin  walls  of  the  oviduct,  composed  of  large  epithelial 
cells,  and  its  wide  cavity  completely  filled  with  round  objects,  each  of  which  is 
an  egg  inclosed  in  a  thick  shell.  Examine  one  of  the  round  objects  with  the 
high  power  and  get  a  clear  idea  of  what  you  are  looking  at.  Identify  in  each 
one  the  thick  shell  inclosing  a  cavity  in  which  floats  the  egg  cell,  considerably 
smaller  than  the  cavity.  The  egg  has  been  fertilized  and  hence  possesses  two 
nuclei,  its  own  nucleus  and  the  nucleus  from  the  sperm.  Its  cytoplasm  is 
vacuolated,  that  is,  appears  to  contain  a  number  of  empty  spaces.  Examine 
the  egg  cells  with  your  highest  power  and  look  for  each  of  the  following  stages 
of  mitosis  (see  Hegner,  p.  29).  Considerable  searching  may  be  required  to  find 
the  various  stages.  Have  the  assistant  help  you.  As  the  sections  are  very  thin, 
only  one  nucleus  may  appear,  or  only  parts  of  the  mitotic  apparatus  may  be 
present.  Avoid  drawing  such  partial  pictures.  Make  your  drawings  large 
and  detailed. 

i.  The  resting  cell. — In  the  so-called  resting  state,  that  is,  the  condition 
before  mitosis  begins,  the  egg  presents  the  same  appearance  as  other  cells  which 
we  have  studied.  It  contains  two1  nuclei,  its  own  and  the  sperm  nucleus.  Each 

'This  is  the  case  only  in  the  fertilized  egg  cell,  not  in  other  cells. 

62 


THE  PROCESS  OF  CELL  DIVISION  63 

of  these  is  a  rounded  vesicle,  inclosing  the  usual  chromatin  granules  and  nuclear 
sap.     Draw  such  a  stage  in  detail.     The  egg  shell  may  be  omitted. 

2.  Spireme  stage  or  early  prophase. — As  cell  division  begins  the  chromatin 
granules  thicken  and  mass  together,  finally  uniting  into  a  long,  coiled  thread, 
called  the  spireme,  which  fills  the  nucleus.     Consider  that  in  sections  only  pieces 
of  such  a  coiled  thread  could  appear.     Look,  therefore,  for  nuclei  containing 
deeply  stained  elongated  pieces  of  chromatin.     At  this  time  also  there  appear 
in  the  cytoplasm  two  dense  collections  of  granules,  called  the  asters.     Each 
aster  has  in  its  center  a  black  granule,  the  centrosome,  and  sends  out  radiations, 
the  astral  rays,  into  the  surrounding  cytoplasm.     A  complete  picture  of  the 
spireme  stage  shows  the  egg  and  sperm  nuclei,  containing  broken  threads  of 
chromatin,  in  contact  with  each  other,  and  an  aster  placed  at  each  end  of  the 
plane  of  contact.     You  may  not  be  able  to  find  a  cell  cut  in  the  right  plane  to 
show  all  of  these  parts  simultaneously.     Draw  in  detail  the  best  example  you 
can  find. 

3.  Late  prophase. — The  spireme  thread  now  breaks  into  a  number  of  distinct 
threadlike  bodies,  each  of  which  is  called  a  chromosome.     In  Ascaris  there  are 
four  of  these.     The  nuclear  membrane  has  disappeared  and  the  chromosomes 
lie  free  in  the  cytoplasm.     They  stain  very  deeply,  and  are  usually  U-shaped. 
Meantime  the  asters  have  drawn  farther  apart  and  delicate  fibrils  extend  between 
them.     These  fibers  are  called  the  spindle,  and  the  whole  structure,  asters  and 
spindle,  is  known  as  the  mitotic  figure.     Draw  a  cell  showing  the  four  chromosomes 
free  in  the  cytoplasm. 

4.  Metaphase. — The  chromosomes-  now  arrange  themselves  in  the  center 
of  spindle.     The  mitotic  figure  is  now  fully  developed  and  symmetrically  placed 
in  the  cell.     Find  a  cell  which  is  cut  parallel  to  the  spindle  and  draw,  showing 
spindle,  asters,  and  the  band  of  chromosomes  across  the  center  of  the  spindle. 
Each  chromosome  has  a  longitudinal  split  at  this  time,  which  is  generally  difficult 
to  see. 

5.  Anaphase. — Each  chromosome  next  splits  in  two  longitudinally  and  the 
two  halves  separate.     One-half  of  each  chromosome  moves  toward  one  aster 
and  the  other  half  to  the  other  aster.     In  this  migration  the  ends  of  the  chromo- 
somes always  point  toward  the  middle  of  the  spindle,  so  that  the  dividing  cell 
in  this  stage  contains  two  groups  of  chromosomes,  each  group  looking  something 
like  the  top  of  a  palm  tree,  with  the  delicate  parallel  threads  of  the  spindle 
stretching  between  them.     Draw. 

6.  Telophase. — The  chromosomes  approach  the  asters,  where  each  group 
condenses  into  a  mass  in  which  the  individual  chromosomes  are  no  longer  dis- 
tinguishable.    A  constriction  which  gradually  pinches  the  cell  into  two  equal 
parts  is  appearing  midway  between  the  two  chromatin  masses.     Draw. 

7.  Completion  of  mitosis. — The  constriction  deepens  dividing  the  cell  into 
two  cells,  the  chromatin  mass  resolves  itself  into  the  ordinary  nuclear  structure, 


64  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

and  a  nuclear  membrane  is  formed.     Two  cells  each  exactly  like  the  original 
single  cell  have  thus  been  produced. 

B.      MITOSIS  IN  PLANT  ROOT  TIPS 

The  root  tips  of  plants  grow  very  rapidly  in  some  cases  and  hence  are  favorable 
places  for  finding  all  the  stages  of  mitosis.  For  this  purpose  longitudinal  sections 
are  made  through  the  root  tip.  The  tip  is  covered  by  a  root  cap  consisting  of 
older  and  hardened  cells,  which  is  pushed  ahead  of  the  real  growing  region.  The 
dividing  cells  are  therefore  found  a  little  distance  back  from  the  tip. 

The  process  of  mitosis  in  these  plant  cells  differs  from  that  seen  in  the  eggs 
of  Ascaris  chiefly  in  that  centrosomes  and  asters  are  entirely  lacking,  so  that  the 
mitotic  figure  consists  of  spindle  only.  Further  differences  are:  in  the  resting 
stages  one  or  more  conspicuous  nucleoli  will  be  found  within  the  nucleus;  the 
spireme  thread  is  closely  coiled  so  that  at  this  stage  the  section  of  the  nucleus 
is  packed  with  small  wormlike  segments  of  the  spireme;  the  chromosomes  are 
numerous  and  less  distinctly  U-shaped;  in  the  anaphase  the  resemblance  of 
each  group  to  the  tops  of  palm  trees  is  quite  striking;  and  in  the  telophase,  the 
new  cell  wall  is  not  produced  by  a  constriction,  but  forms  in  place,  apparently 
in  part  from  a  condensation  of  the  spindle  fibers.  The  spindle  is  rather  faint 
throughout  and  is  seen  best  only  in  the  late  stages  of  mitosis. 

C.      MITOSIS  IN  THE  EGGS   OF  THE  WHITEFISH 

The  sections  are  taken  through  the  dividing  eggs  of  the  fish,  generally  in 
the  early  stages  when  the  cells  are  quite  large.  Each  section  shows  a  number  of 
cells,  some  of  which  will  be  found  to  be  in  various  stages  of  mitosis.  Differences 
from  Ascaris  are  that  the  chromosomes  are  quite  small,  very  numerous,  and 
rodlike  in  form;  and  that  a  number  of  minute  centrosomes  instead  of  the  one 
large  centrosome  of  Ascaris  are  present.  They  are  difficult  to  see.  A  clear 
field  surrounds  the  place  occupied  by  the  centrosomes,  and  from  this  the  long 
fibers  of  the  asters  radiate  nearly  filling  the  cell.  Fish  eggs  are  valuable  for  the 
study  of  mitosis  chiefly  because  the  mitotic  figure  is  of  such  large  size  and  so 
distinctly  fibrillar  in  them  that  they  present  a  striking  appearance,  which  closely 
corresDonds  to  the  textbook  representations  of  this  structure. 


VH.     GENERAL  EMBRYOLOGY 

The  egg  cell,  after  the  sperm  cell  has  penetrated  it  (process  of  fertilization) 
enters  on  a  process  of  development,  the  study  of  which  constitutes  the  subject 
of  embryology.  An  elementary  study  of  embryonic  development  will  be  made 
first  on  a  simple  case  like  that  of  the  starfish  (Asterias),  then  on  the  more  com- 
plicated case  of  the  frog  (Hegner,  pp.  107-111). 

A.      DEVELOPMENT  OF  THE   STARFISH 

The  fertilized  egg  first  divides  by  mitosis  a  number  of  successive  times  until 
a  large  number  of  very  small  cells  is  produced.  This  part  of  development  is 
called  cleavage  or  segmentation.  Study  slide  "Asterias — early  cleavage."  Note 
that  the  objects  on  the  slide  are  not  sections  but  the  entire  cells.  (The  cells 
which  exhibit  a  large  clear  nucleus  containing  a  black  spot  [nucleolus]  are  unfer- 
tilized eggs).  Each  egg  and  embryo  is  surrounded  by  a  membrane,  which  is 
called  the  fertilization  membrane,  and  is  separated  from  the  egg  at  the  time  of 
fertilization. 

1.  Two-celled  stage. — The  egg  divides  into  two  equal  halves,  which  remain 
in  contact  with  each  other.     Find  and  draw  in  outline. 

2.  Four-celled  stage. — A  second  division  occurs  at  right  angles  but  passing 
through  the  same  axis  as  the  first.     Draw. 

3.  Eight-celled  stage. — Each  cell  of  the  four-celled  stage  divides  in  two 
transversely  at  right  angles  to  both  the  previous  divisions,  producing  eight 
equal  cells  in  two  plates  of  four  cells  each.     Find  and  draw.    Note  that  the 
cells  may  easily  become  displaced  from  their  natural  position  in  the  making 
of  the  slide,  and  pick  out  only  those  that  present  the  normal  appearance. 

4.  Later  cleavage. — Examine  slide  "Asterias — late  cleavage."    The  process 
of  division  continues  until  a  large  number  of  cells  is  produced.    Meantime,  a 
central  cavity  appears  between  the  cells. 

5.  Blastula. — Examine  slide  "Asterias — blastula  or  larval  stages."    At  the 
end  of  the  cleavage  process,  the  embryo  consists  of  a  single  layer  of  cells  sur- 
rounding a  central  large  cavity,  the  segmentation  cavity.    This  stage  is  the 
blastula.     Its  form  is  that  of  a  rubber  ball.     Find  one  of  these  balls  of  small 
cells,  and  focus  so  as  to  obtain  an  optical  section,  i.e.,  focus  so  that  the  appearance 
is  the  same  as  if  you  had  actually  made  a  section  through  the  center  of  the 
blastula.     In  such  a  focus  the  blastula  appears  as  a  circular  layer  of  cells, 
the  layer  being  one  cell  thick,  surrounding  a  large  cavity.     Draw  the  optical 
section. 

65 


66  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

6.  Gastrula. — Examine  slide  "Asterias — gastula  or  larval  stages."  This 
stage  marks  the  end  of  the  cleavage  stage  (although  of  course  cell  division  con- 
tinues) and  the  beginning  of  differentiation.  The  gastrula  arises  from  the  blastula 
by  the  pushing  in  of  one  wall  just  as  if  one  should  thrust  one's  finger  into  the 
side  of  a  rubber  ball.  The  gastrula  appears  on  the  slide  as  an  oval  body,  contain- 
ing a  central  darker  projection.  Find  one  in  profile,  obtain  an  optical  focus  on 
it  and  draw.  The  outer  layer  of  cells  is  called  the  ectoderm;  the  inner  layer, 
which  has  been  pushed  in  or  invaginated,  the  entoderm;  the  entire  invaginated 
structure  is  the  archenteron,  or  primitive  intestine;  and  the  opening  of  the 
archenteron  to  the  outside  is  the  Uastopore.  The  next  step  in  development  is 
the  formation  of  a  third  layer  of  cells,  the  mesoderm,  between  the  ectoderm  and 
entoderm,  and  these  three  layers  are  called  germ  layers  because  from  them  all  the 
structures  of  the  adult  organism  are  derived. 


B.      DEVELOPMENT   OF  THE  FROG 

Preserved  material  will  be  provided  for  this  purpose.  Remove  the  jelly 
from  the  eggs.  Consult  Holmes,  chapter  v,  pp.  89-103. 

1.  Cleavage  stages. — The  egg  of  the  frog  is  much  larger  than  that  of  the 
starfish  because  it  contains  a  considerable  quantity  of  yolk,  a  semifluid  food 
material  containing  proteins  and  fats.     The  egg  is  black  and  white,  the  black 
half  constituting  the  animal  hemisphere  and  consisting  largely  of  protoplasm, 
while  the  white  half,  the  vegetative  hemisphere,  holds  most  of  the  yolk.     Owing 
to  the  presence  of  yolk,  the  vegetative  hemisphere  divides  more  slowly  and 
produces  larger  cells  than  the  animal  hemisphere. 

Study  with  the  low  power  or  with  a  hand  lens  and  draw  two-,  four-,  and 
eight-cell  stages.  Note  the  inequality  in  the  size  of  cells  of  the  two  hemispheres, 
and  the  tendency  of  the  vegetative  cells  to  lag  behind,  so  that  six  cell  stages  may 
occur. 

2.  Blastula. — After  numerous  cleavages  a  blastula  is  produced  consisting  of 
numerous  very  small  black  cells,  and  less  numerous  larger  white  cells.     Draw. 
Then  with  a  sharp  knife  bisect  the  blastula  by  a  cut  which  cleaves  the  black  and 
white  hemispheres,  and  examine  the  cut  surface  with  a  hand  lens.     Compare 
with  Holmes,  Fig.  18  (p.  93),  and  draw.     The  blastula  of  the  frog  differs  from 
that  of  the  starfish  in  that  its  wall  is  composed  of  several  layers  of  cells. 

3.  Gastrula  or  yolk  plug  stage. — Owing  to  the  large  amount  of  inert  yolk 
in  the  white  cells,  they  cannot  invaginate  as  in  the  case  of  the  starfish,  but  the 
gastrula  is  formed  mainly  by  the  growth  and  extension  of  a  sheet  of  black  cells 
down  over  the  white  cells.     The  white  cells  are  thus  inclosed  and  become  the 
entoderm.     The  closure  of  the  black  cells  over  the  white  is  not  quite  complete, 
leaving  a  circular  opening,  the  blastopore,  through  which  some  of  the  white  cells 
protrude,  producing  a  circular  white  area,  the  yolk  plug.     Draw,  showing  the 


GENERAL  EMBRYOLOGY  67 

blastopore  and  yolk  plug.  Bisect  the  gastrula  by  a  cut  through  the  yolk  plug 
and  the  center  of  the  black  hemisphere.  Examine  the  cut  surface,  compare 
with  Holmes's  Figs.  19  and  20  (pp.  94  and  96),  and  draw.  The  black  cells  are 
the  ectoderm,  the  white  cells,  the  entoderm,  and  about  this  time  a  third  layer, 
the  mesoderm,  begins  to  grow  out  between  the  ectoderm  and  entoderm  from  the 
cells  around  the  blastopore. 

4.  Origin  of  the  nervous  system;   neural  fold  stage. — Examine  embryos  of 
this  stage  with  a  lens  and  note  that  a  fold  is  appearing  on  each  side  of  a  central 
groove  extending  lengthwise  along  the  black  hemisphere.    This  groove  marks 
the  dorsal  median  line  of  the  future  embryo.    The  pair  of  folds,  the  medullary  folds, 
later  come  in  contact  and  fuse  in  the  median  dorsal  line,  thus  forming  a  longitudi- 
nal tube  which  is  the  central  nervous  system.     The  blastopore  is  now  reduced 
to  a  small  hole.     Draw.    Holmes's  Fig.  22  (p.  98)  is  a  cross-section  of  this  stage. 

5.  Mesoderm  and  coelome. — Examine  slide.    This  is  a  cross-section  of  a 
stage  about  halfway  between  Holmes's  Figs.  22  and  26.     The  cross-section  is 
roughly  pear-shaped,  the  narrow  end  of  the  section  being  the  dorsal  side  of  the 
embryo.     The  section  is  surrounded  by  a  layer  of  uniform  width,  two  or  three 
cells  thick.     This  is  the  ectoderm,  destined  to  become  the  epidermis  of  the  skin. 
In  the  dorsal  median  line  just  under  the  ectoderm  is  an  oval  mass  of  cells  with  a 
central  elongated  cavity.     This  is  the  cross-section  of  the  neural  tube  or  central 
nervous  system,  which,  as  has  been  seen,  originates  as  a  pair  of  ectodermal  folds, 
which  then  umte  to  form  a  tube,  while  the  ectoderm  fuses  again  over  the  tube 
to  a  continuous  layer.     Just  ventral  to  the  tube  is  a  circular  mass,  the  notochord, 
which  arises  by  an  upfolding  of  the  dorsal  wall  of  the  intestine.     It  is  a  long, 
slender  rod,  around  which  the  vertebrae  later  develop.     Ventral  to  the  notochord 
appears  the  primitive  intestine,  a  large,  nearly  circular,  mass  of  ill-defined  cells. 
Its  dorsal  wall  is  thin  and  overlies  a  cavity,  the  cavity  of  the  future  digestive 
tract;  its  ventral  wall  is  very  thick  on  account  of  the  yolk  which  it  contains. 
This  intestine  is  the  entoderm,  and  its  cells  become  the  lining  epithelium  of  the 
digestive  tract.     Between  the  ectoderm  and  the  entoderm  lies  the  mesoderm; 
it  consists  of  a  large  triangular  mass  of  cells  on  each  side  of  the  neural  tube  from 
which  a  layer  of  cells  extends  ventrally  on  either  side  of  the  intestine,  meeting 
below.     The  layer  of  mesoderm  cells  generally  shows  a  central  split,  which  is  the 
coelome.     The  mesoderm  to  the  outer  side  of  the  split,  next  to  the  ectoderm, 
then  represents  the  parietal  layer  of  the  peritoneum  and  some  of  the  connective 
tissue  of  the  body  wall.     The  mesoderm  on  the  inner  side  of  the  split,  next 
to  the  entoderm  is  destined  to  form  the  connective  tissue  and  muscular  layers 
of  the  wall  of  the  digestive  tract,  the  visceral  layer  of  peritoneum,  and  the 
mesenteries.     The  masses  of  mesoderm  at  the  sides  of  the  neural  tube  and 
notochord  form  the  axial  skeleton,  nearly  all  of  the  voluntary  muscles,  and  the 
dermis  of  the  skin.     The  mesoderm  immediately  ventral  to  the  triangular  mass 
is  the  source  of  the  urinogenital  system. 


68  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

Draw  the  cross-section.  Do  not  attempt  to  put  in  individual  cells,  as  these 
are  not  distinctly  visible. 

6.  Later  development  and  segmentation. — Examine  with  the  hand  lens 
embryos  of  about  the  stages  of  Holmes's  Fig.  24  (p.  101)  and  Fig.  30, 3  (p.  117). 
Note  the  elongation  of  the  body  with  later  appearance  of  a  tail.  In  the  younger 
embryo  observe  that  the  nervous  system  is  sharply  marked  off  along  the  whole 
dorsal  side  and  that  grooves,  later  to  break  through  as  gill  slits,  are  present  on 
the  sides  of  the  head.  In  the  older  embryo  identify  the  eyes  on  the  sides  of  the 
head,  the  ventral  mouth  with  horny  lips,  the  two  suckers  posterior  to  the  mouth, 
and  the  much-coiled  intestine  visible  through  the  skin.  Note  especially  in  the 
tail  the  zigzag  segments.  Each  such  segment  is  a  unit  of  structure  and  will  give 
rise  to  a  vertebra,  a  section  of  the  spinal  cord  with  a  pair  of  spinal  nerves,  a 
certain  number  of  muscles,  paired  branches  of  the  chief  blood  vessels,  etc.  These 
segments  are  also  present  in  the  body  region  of  the  tadpole,  although  externally 
invisible.  Segmentation,  that  is,  repetition  of  structures  along  the  axis,  in 
fact  underlies  the  whole  make-up  of  the  adult  frog. 


VIII.     HEREDITY:    MENDEL'S  LAW 

In  the  experiment  on  the  life-cycle  of  the  fruit  fly  (Drosophila)  you  were 
given  a  pair  of  flies  which  differed  from  each  other  in  a  single  character,  as  long 
wings  and  short  wings.  (If  blowflies  were  provided  for  that  experiment,  a  pair 
of  fruit  flies  will  now  be  given  to  you  and  should  be  examined  according  to  the 
directions  under  II,  F,  i.)  The  offspring  resulting  from  such  a  pairing  between 
unlike  individuals  are  therefore  hybrids,  and  it  becomes  a  matter  of  great  interest 
to  find  out  what  will  be  the  appearance  of  the  offspring,  as  we  may  then  discover 
how  the  characters  of  animals  behave  in  heredity. 

A.      FIRST  HYBRID  GENERATION 

When  the  offspring  appear  note  carefully  the  character  of  the  wings  (or  other 
feature  which  was  selected  for  the  experiment).  Are  they  all  alike,  or  of  two 
kinds,  like  the  parents,  or  do  they  resemble  one  parent  more  than  the  other,  or 
are  they  intermediate?  What  is  the  meaning  of  the  terms  "dominant"  and 
"recessive"  as  applied  to  a  pair  of  characters  such  as  we  are  dealing  with  here  (A)? 

A  fresh  bottle  with  banana  will  be  provided  for  each  student  into  which  he  is 
to  put  one  or  two  pairs  of  flies  from  his  first  generation  and  raise  a  second  genera- 
tion. The  transference  of  the  flies  may  be  accomplished  by  dropping  a  small  bit 
of  cotton  soaked  in  ether  into  the  bottle  and  taking  out  the  flies  after  they  have 
become  unconscious,  or  by  holding  a  bottle  over  the  end  of  the  old  culture  bottle 
until  a  few  flies  have  flown  into  it,  then  holding  the  bottle  over  the  new  culture 
bottle  until  they  have  flown  out  again.  In  doing  this  make  use  of  the  tendency 
of  Drosophila  to  fly  toward  the  light. 

B.      SECOND  HYBRID   GENERATION 

In  the  second  hybrid  generation  note  again  the  character  of  the  wings  (or 
other  feature  selected)  and  determine  the  number  of  individuals  with  each  kind 
of  wing  length.  This  behavior  of  a  hereditary  character  is  called  Menders 
law  or  alternative  inheritance.  If  we  suppose  that  every  female  fly  of  the  first 
hybrid  generation  gave  rise  to  two  kinds  of  eggs  in  equal  numbers,  one  bearing 
the  character  "long  wings"  and  the  other  the  character  "short  wings";  and  that 
similarly  every  male  of  the  first  hybrid  generation  produced  two  kinds  of  sperms 
in  equal  numbers;  and  that  in  fertilization  all  possible  chance  combinations 
occurred  (i.e.,  each  kind  of  sperm  fertilizes  both  kinds  of  eggs),  what  kind  and 
proportions  of  offspring  would  we  expect  mathematically?  Thus  if  L  is  taken 
to  represent  the  character  "long  wings"  and  5  the  character  "short  wings"  we 

69 


70  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

get  as  a  result  of  algebraic  multiplication  the  following  possible  combinations  in 
equal  numbers:  LL,  Ls,  Ls,  ss.  What  will  be  the  external  appearance  of  the 
flies  containing  each  of  these  combinations?  Will  LL  differ  from  Ls?  Why? 
What  then  will  be  the  ratio  of  long-  to  short-winged  individuals  in  the  second 
generation  (Hegner,  p.  289)? 

These  experiments  were  first  performed  by  a  monk  named  Mendel,  who 
made  crosses  between  different  varieties  of  peas  in  the  garden  of  the  monastery 
at  Briinn,  Austria.  He  discovered  that  in  such  crosses  the  differences  between 
the  two  plants  that  are  crossed  do  not  become  permanently  blended  in  the 
offspring  but  separate  out  again  unchanged  in  the  second  generation.  This 
behavior  of  the  characters  in  crossing  two  different  organisms  is  called  Mendel's 
law,  and  Mendel's  results  have  since  been  confirmed  on  a  very  large  number  of 
plants  and  animals.  The  conclusion  which  has  been  drawn  from  these  experi- 
ments is  that  the  characteristics  of  animals  are  separate;  that  they  are,  so  to 
speak,  independent  units,  which  exist  in  some  fashion  or  other  as  units  in  the 
eggs  and  sperms;  that  these  units  remain  separate  hi  a  hybrid  organism  even 
though  the  hybrid  may  appear  externally  to  be  a  blend  of  the  characters  of  its 
two  unlike  parents;  and  that  under  proper  circumstances  they  may  be  made 
to  separate  out  again  apparently  unchanged.  Modern  research  indicates  thai 
the  unit  characters  or,  more  correctly  speaking,  materials  which  represent  the 
unit  characters  are  located  in  the  chromatin  of  the  nucleus. 


IX.     PHYLUM  PROTOZOA 

A.      INTRODUCTORY  REMARKS 

In  the  preceding  sections  of  this  manual  we  have  studied  in  detail  the  anatomy 
of  a  fairly  complex  animal,  the  frog.  We  have  seen  the  systems  of  organs  of 
which  the  frog  is  composed,  the  cells  and  tissues  which  are  the  framework  of 
these  organs,  and  for  what  purpose  and  in  what  manner  these  organs  are  used 
in  enabling  the  animal  to  continue  its  existence.  We  have  further  seen  that  all 
of  this  complicated  mechanism  arises  from  a  single  undifferentiated  cell,  the  egg, 
which,  stimulated  to  activity  by  the  entrance  into  its  substance  of  a  sperm, 
starts  on  a  process  of  development  in  the  course  of  which  the  multitude  of 
structures  found  in  the  adult  animal  come  into  existence. 

In  this  course  of  development  in  animals  we  further  note  that  certain  funda- 
mental steps  are  involved.  First  the  egg  proceeds  to  produce  a  large  number  of 
apparently  similar  undifferentiated  cells  by  the  process  of  cell  division,  which 
we  also  studied.  This  continues  until  a  ball  of  cells  is  produced.  Then  occurs 
the  first  step  in  differentiation;  part  of  the  ball  invaginates  so  that  a  layer  of 
cells,  now  called  the  entoderrn,  lies  within  another  layer  of  cells,  the  ectoderm. 
So  important  are  these  layers  for  the  future  development  that  they  are  designated 
as  germ  layers,  i.e.,  layers  from  which  certain  systems  are  to  arise.  Owing  to 
their  different  positions  these  two  layers  have  different  relations  to  the  external 
environment  and  hence  must  take  on  different  functions.  The  ectoderm,  being 
in  contact  with  the  environment,  must  necessarily  receive  stimuli  from  this 
environment  and  act  as  protection  against  the  harmful  conditions  which  may 
arise;  hence  it  is  destined  for  nervous  and  covering  structures.  The  entoderrn 
naturally  takes  on  digestive  functions,  since  food  is  essential  to  life,  and  an 
animal  can  hardly  digest  food  unless  it  takes  the  food  into  its  interior.  This 
structural  condition  found  in  the  gastrula  stage  of  development  is  known  as 
diplobastic  (meaning  two  germ  layers),  and,  as  we  shall  see,  thousands  of  animals 
exist  whose  structure  has  gone  no  farther  than  this.  However,  it  is  obvious  that 
no  very  great  degree  of  complexity  and  differentiation  can  be  attained  in  a  gas- 
trula; a  third  germ  layer,  the  mesoderm,  next  arises  between  the  other  two,  from 
which  is  produced  by  far  the  greater  part  of  the  structures  that  we  have  seen  in 
the  frog.  This  condition  is  known  as  triploblastic  (meaning  three  germ  layers). 
The  next  advance  is  the  splitting  of  the  mesoderm,  so  as  to  leave  a  cavity,  the 
coelome,  between  its  two  layers;  and  finally  the  mesoderm  becomes  segmented, 
that  is,  repeats  itself  along  the  axis. 

Having  thus  established  in  our  minds  a  fairly  complete  picture  of  the  make-up 
of  an  animal  and  the  manner  in  which  its  anatomical  features  have  come  into 


72  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

existence,  we  shall  next  study  a  number  of  other  common  animals,  comparing 
them  with  the  frog  in  structure,  histology,  and  function.  Just  as  the  frog 
forms  one  of  a  great  group  of  animals,  the  vertebrates,  distinguished  by  the  posses- 
sion of  a  vertebral  column,  so  all  the  animals  which  exist  upon  the  earth  can  be 
arranged  into  great  groups,  each  of  which  is  called  a  phylum.  There  are  about 
a  dozen  of  these  phyla  and  they  are  distinguished  from  each  other  very  easily 
by  large  important  anatomical  differences.  We  shall  study  representatives  of 
several  of  these  phyla,  starting  with  the  simplest,  always  comparing  their  anatomy 
with  that  of  the  frog  and  seeing  how  one  by  one  the  systems  of  which  the  frog 
is  composed  have  come  into  existence. 

We  trust  the  student  has  by  this  time  been  sufficiently  impressed  with  the 
fact  that  the  unit  of  structure  of  the  frog  is  the  cell  and  that  the  entire  frog  comes 
from  one  cell.  We  are  now  about  to  see  that  numerous  adult  animals  exist 
which  consist  of  but  a  single  cell,  but  yet  are  able  to  carry  on  all  of  the  functions 
necessary  to  life  within  the  limits  of  this  single  cell.  These  animals  belong  to 
the  phylum  Protozoa,  or  the  one-celled  animals.  They  are  the  simplest  animals, 
and  one  of  the  simplest  among  them  is  the  one  to  which  we  shall  first  direct  our 
attention,  the  Amoeba.  Read  Hegner,  chapter  iv,  pp.  37-53. 


B.      THE  AMOEBA 

1.  General  structure  and  locomotion. — Mount  a  few  drops  of  solid  material 
from  the  culture  on  a  slide,  cover,  and  examine  with  the  low  power.     Cut  down 
the  light.     Search  the  slide  for  an  irregular  granular  object,  apparently  motionless. 
Ask  the  assistant  whether  or  not  you  have  an  Amoeba  or  have  him  help  you  find 
one.     Study  the  animal  with  both  low  and  high  powers.     Observe  that  the 
Amoeba  moves  by  putting  out  projections,  called  pseudopodia,  from  its  surface 
and  then  flowing  into  these  projections.     This  type  of  movement  is  designated 
as  amoeboid  movement.     The  protoplasm  of  the  Amoeba  may  be  divided  into  two 
regions,  an  outer  clear  layer,  the  ectoplasm,  entirely  free  from  granules,  and  the 
central  mass,  the  endoplasm  (also  spelled  "entoplasm"),  filled  with  round  or 
dark  oval  granules,  of  unknown  function,  and  food  particles.     Under  the  high 
power  watch  the  formation  of  a  pseudopodium,  and  determine  how  the  ectoplasm 
and  endoplasm  behave  in  its  formation.     Does  the  Amoeba  have  anterior  and 
posterior  ends  or  a  definite  form? 

Make  five  outline  drawings  of  the  Amoeba  to  show  successive  changes  of 
shape.     Indicate  by  arrows  the  direction  of  flow  of  the  protoplasm. 

2.  Special  structures. — Find  a  specimen  whose  protoplasm  is  well  spread 
out  and  not  excessively  granular  and  look  with  the  high  power  for  the  following 
structures: 

a)  The  contractile  vacuole:  Watch  the  non-moving  parts  of  the  animal  for  a 
perfectly  spherical  clear  spot.     At  intervals  it  contracts  and  disappears,  hence 


PHYLUM  PROTOZOA  73 

the  name  contractile  vacuole.  If  you  have  a  favorable  specimen,  watch  and 
describe  in  your  notes  the  behavior  of  the  vacuole,  and  time  the  interval  between 
contractions.  When  the  vacuole  reappears  after  a  contraction,  is  it  the  same 
size  as  previously?  Sometimes  two  or  more  vacuoles  may  be  present,  but  they 
generally  coalesce  into  one  later.  What  is  the  function  of  the  contractile 
vacuole  (R)? 

b)  The  nucleus:    This  is  a  sharply  outlined,  finely  granular  body  in  the 
neighborhood  of  the  contractile  vacuole,  often  in  contact  with  it  and  of  about  the 
same  size  as  the  fully  expanded  vacuole.     Its  granules,  which  are  chromatin 
granules,  are  much  finer  and  more  regularly  distributed  than  those  of  the  endo- 
plasm.     Determine  the  real  shape  of  the  nucleus  by  watching  it  as  it  rolls  along 
in  the  moving  endoplasm.     Is  it  spherical?     Occasionally  specimens  are  found 
which  have  two  nuclei. 

c)  Food  vacuoles:    The  endoplasm  usually  contains  particles  or  masses  of 
digesting  food,  the  larger  of  which  may  be  inclosed  in  a  drop  of  fluid  and  hence 
are  called  food  vacuoles.     Find  out  in  your  text  how  the  Amoeba  digests  food. 
How  does  the  process  compare  with  that  of  the  frog? 

Make  an  enlarged  drawing  of  the  Amoeba,  and  put  into  it  all  of  the  details 
of  structure  described  above.  Indicate  the  granular  appearance  by  stippling 
with  the  pencil  point. 

4.  Activities. — Can  you  observe  any  indications  that  the  amoeba  is  irritable 
and  responds  to  the  varying  conditions  of  its  environment?    For  instance,  what 
does  it  do  when  it  comes  in  contact  with  an  obstacle  or  when  other  animals 
strike  against  it?     If  possible,  observe  the  reaction  to  food  material.     How  do 
you  suppose  the  amoeba  distinguishes  between  food  particles  and  other  particles? 
What  does  the  amoeba  do  when  it  comes  in  contact  with  food  material?    Describe 
in  your  notes  and  sketch  this  behavior,  if  you  are  so  fortunate  as  to  observe  it. 

5.  General  considerations  on  the  amoeba. — Does  the  amoeba  carry  on  all 
the  physiological  processes  that  we  found  to  occur  in  the  frog?    Does  it  have 
any  special  organs  for  these  processes?    What  are  the  significant  differences  and 
resemblances  between  the  amoeba  and  the  frog?    What  does  the  frog  gain  by 
its  greater  complexity  of  structure?    To  what  stage  in  development  of  the  frog 
does  the  amoeba  correspond?     Give  these  questions  careful  thought  and  answer 
specifically  in  your  notes. 

C.      PARAMECIUM 

The  study  of  this  animal  is  usually  somewhat  difficult  owing  to  its  swift 
movements.  In  order,  therefore,  to  obtain  satisfactory  results  the  student  must 
follow  the  directions  very  closely  (Hegner,  chap,  v,  pp.  59-79)- 

i.  General  form  and  movements. — Mount  a  solid  piece  of  scum  and  a  drop 
of  water  from  the  culture  on  a  slide  and  examine  under  the  low  power  without 
a  cover  glass.  A  number  of  different  organisms  will  probably  be  present  and 


74  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

of  these  the  relatively  large,  greenish,  slipper-shaped  animals  are  Paramecia. 
Note  carefully  the  general  shape  of  the  body.  Are  the  two  ends  different  in 
form?  Is  one  end  always  directed  forward  in  swimming?  If  so,  which  end? 
Does  the  animal  have  a  definite  permanent  shape? 

Watch  and  describe  in  your  notes  the  swimming  movements.  Observe  that 
the  animal  when  swimming  in  a  free  field  revolves  upon  its  long  axis;  also  it 
seems  to  swerve  from  side  to  side.  What  is  the  cause  of  the  rotation  and  the 
swerving  and  what  is  the  real  path  of  the  animal  (see  Hegner,  p.  65)? 

By  this  time  the  student  will  probably  have  observed  that  the  animal  is 
not  symmetrical  and  cylindrical  but  that  the  anterior  half  is  deeply  concave 
as  if  a  large  slice  had  been  cut  out  of  it.  This  concave  depression  is  called  the 
oral  groove.  It  is  best  seen  by  watching  the  animals  as  they  revolve.  The  side 
of  the  Paramecium  on  which  the  oral  groove  is  located  is  the  ventral  or  oral 
side;  the  opposite  side,  the  dorsal  or  aboral  surface;  and  right  and  left  are  then 
easily  determined.  (In  Hegner,  Fig.  23,  p.  60,  the  labels  R  and  L  have  been 
interchanged.)  Observe  the  freely  moving  animals  carefully  until  you  have 
obtained  a  correct  idea  of  the  width,  length,  and  direction  of  slant  of  the  oral 
groove.  How  wide  is  it  compared  with  the  anterior  end?  Does  it  slant  from 
right  to  left  or  left  to  right?  (Remember  that  as  the  animal  is  transparent  you 
cannot  determine  whether  you  are  looking  at  the  upper  or  under  side  of  it,  except 
by  the  use  of  the  focusing  screw.)  How  far  posteriorly  does  it  extend  f 

Make  an  outline  drawing  of  the  animal  from  the  ventral  side,  about  four 
inches  long,  showing  its  correct  shape  and  proportions  and  correct  appearance 
of  the  oral  groove.  Have  the  drawing  approved  by  the  assistant  before  proceed- 
ing. The  details  of  structure  are  later  to  be  entered  upon  this  outline. 

2.  Detailed  structure. — This  study  must  be  made  with  the  high  power,  a 
proceeding  usually  fraught  with  difficulty  for  the  student  because  the  animal 
will  not  stand  still.  One  or  all  of  the  following  methods  of  quieting  the  animals 
must  therefore  be  employed  and  will  ordinarily  prove  successful:  (i)  Always 
mount  the  animals  with  a  piece  of  scum  or  other  solid  material  from  the  culture. 
They  will  generally  remain  quiet  around  this,  or  around  air  bubbles,  or  often 
near  the  edge  of  the  cover  glass.  This  is  the  most  satisfactory  method  of  study- 
ing Paramecium^  as  the  animals  remain  in  a  normal  condition  throughout. 
Every  student  should  try  this  first.  (2)  Withdraw  the  water  from  the  slide 
by  applying  a  piece  of  filter  paper  to  the  edge  of  the  cover  glass,  so  that  not 
enough  water  remains  for  the  animals  to  swim  in.  Under  these  conditions, 
however,  the  normal  shape  and  appearance  of  the  animals  is  lost,  and  they  soon 
burst  and  die  so  that  observations  must  be  completed  quickly.  (3)  Mount  a 
drop  or  two  of  Paramecium  on  a  slide  and  place  in  the  center  a  small  drop  of  a 
very  dilute  solution  of  formaldehyde.  Cover.  The  animals  near  the  formalde- 
hyde will  soon  slow  down  and  finally  become  entirely  motionless;  those  farther 
away  will  eventually  also  succumb.  For  a  time,  the  motionless  animals  retain 


PHYLUM  PROTOZOA 


75 


the  normal  shape  and  structure  (although  the  trichocysts  are  often  discharged), 
but  finally  they  round  up  and  become  abnormal.  When  this  happens  find 
another  specimen.  This  method  is  very  successful,  provided  that  the  proper 
concentration  of  formaldehyde  is  used. 

All  observations  with  the  high  power  must  be  made  with  a  cover  glass  over 
the  material.  Do  not  allow  the  material  to  dry  up.  Make  observations  only 
upon  normal  specimens,  as  far  as  practicable.  With  a  little  patience  all  of  the 
following  details  of  structure  can  be  observed. 

Paramecium,  like  Amoeba,  consists  of  but  a  single  cell,  but  whereas  the  latter 
is  a  mass  of  nearly  homogeneous  protoplasm,  showing  little  differentiation,  the 
protoplasm  of  Paramecium  has  become  differentiated  into  a  considerable  number 
of  different  parts,  as  the  following  description  will  demonstrate. 

a)  Ectosarc:  The  outer  layer  of  protoplasm  of  the  Paramecium  is  called  the 
ectoplasm  or  ectosarc.     The  surface  of  the  ectosarc  is  differentiated  as  a  firm 
membrane,  the  cuticle  or  pellicle,  to  which  the  animal  owes  its  permanent  shape. 
It  is  marked  with  a  mosaic  of  hexagons  which  is  not  usually  demonstrable  (see 
Hegner,  Fig.  24,  p.  62).     From  all  over  the  cuticle  arise  delicate  threadlike 
processes  of  the  protoplasm,  the  cilia,  whose  co-ordinated  movement  like  numer- 
ous little  oars  propels  the  animal  through  the  water.     The  cilia  are  practically 
of  the  same  length  over  the  body  except  that  there  is  a  tuft  of  longer  ones  on  the 
posterior  extremity.     Those  in  the  oral  groove  are  especially  active.     The  cilia 
are  best  seen  by  focusing  on  the  edge  of  the  animal.     The  layer  of  ectoplasm 
under  the  cuticle  contains  innumerable  rodlike  bodies  lying  parallel  to  each 
other  and  at  right  angles  to  the  surface.     They  are  best  seen  by  focusing  on  the 
edge  of  the  animal,  as  in  the  central  parts  01  the  animal  they  are  viewed  from 
the  end  and  hence  appear  as  dots.     They  are  called  trichocysts  and  appear  to  be 
little  oval  sacs  containing  a  viscous  fluid.     Upon  stimulation  this  fluid  is  dis- 
charged through  the  minute  opening  of  the  trichocyst  and  hence  is  squeezed 
out  into  the  form  of  a  long  thread.     Enter  the  layer  of  trichocysts  and  the  cilia 
upon  your  outline  drawing.     Do  not  make  a  new  drawing. 

b)  Endosarc:    The  central  mass  of  the  Paramecium  is  the  endoplasm  or 
endosarc.     It  is  much  more  fluid  than  the  ectosarc  and  is  filled  with  granules. 
It  generally  contains  a  number  of  spherical  vacuoles  packed  with  food  particles, 
designated  as  food  vacuoles.     It  contains  the  nuclei  (see  below).     Enter  details 
of  the  endoplasm  on  your  drawing. 

c)  Digestive  apparatus:  This  is  best  studied  on  a  normal  active  animal,  one 
that  is  resting  quietly  near  some  object.     It  can  also  be  seen  on  formalized 
animals  but  not  on  those  which  have  been  flattened  out  by  withdrawal  of  water. 
Having  found  a  favorable  individual,  watch  the  posterior  end  of  the  oral  groove 
(be  sure  you  know  where  this  is)  for  an  oval  clear  spot.    This  is  the  so-called 
mouth.     Then  observe  a  clear  funnel-shaped  curved  cavity  leading  posteriorly 
from  the  mouth  down  into  the  endoplasm.     This  is  the  gullet  or  cytopharynx. 


76  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

In  favorable  cases  you  may  observe  minute  food  particles  shooting  down  the 
gullet  and  collecting  into  balls  in  its  inner  rounded  end.  Note  the  great  activity 
of  the  cilia  in  the  gullet,  where  they  are  fused  into  a  vibrating  membrane,  known 
as  the  undulating  membrane.  The  oral  groove,  mouth,  gullet,  and  undulating 
membrane  are  the  food-catching  apparatus  of  the  Paramecium.  Near  the  gullet 
is  a  region  inappropriately  named  the  anus,  where  undigested  food  material  is 
extruded.  It  can  be  seen  only  when  material  is  passing  out  through  it.  (The 
terms  "mouth/5  "pharynx,"  "anus,"  etc.,  should  not  have  oeen  applied  to  the 
Paramecium  as  they  do  not  in  the  least  correspond  to  the  structures  so  named 
in  the  frog,  except  from  the  point  of  view  of  their  function.)  Enter  the  above- 
mentioned  details  on  your  drawing. 

d)  Contractile  vacuoles:   Observe  a  circular  clear  spot  near  each  end  of  the 
animal.     These  are  the  contractile  vacuoles.     They  are  located  between  the 
ectosarc  and  the  endosarc  but  firmly  attached  to  the  former.     Are  they  on  the 
ventral  or  dorsal  side?    Watch  the  contraction  and  note  the  radiating  canals 
which  appear  like  the  petals  of  a  flower  around  the  point  where  the  vacuole  has 
disappeared.     What  is  the  average  time  between  successive  contractions  of  a 
vacuole?    How  does  this  compare  with  the  contraction  interval  of  the  vacuole 
of  Amoeba?    The  anterior  vacuole  of  Paramecium  generally  contracts  more 
frequently  than  the  posterior  one.     (Note  that  the  vacuoles  may  cease  to  con- 
tract or  may  contract  very  slowly  in  formalized  specimens,  and  become  very 
large  and  abnormal  in  behavior  in  flattened  specimens.)     Enter  vacuoles  and 
canals  on  your  drawing. 

e)  Nuclei:  Paramecium  and  its  relatives  have  two  nuclei,  a  large  meganucleus 
(also  called  macronucleus)  and  a  small  micronucleus.    They  cannot  be  seen  in 
normal  animals,  but  the  meganucleus  can  usually  be  recognized  as  a  central 
large  irregular  mass  in  flattened  and  formalized  individuals.     Study  the  nuclei 
in  the  stained  slides  of  Paramecium  which  are  in  your  box.     The  meganucleus 
is  a  large-lobed  and  folded  mass  in  or  near  the  center,  and  the  micronucleus  is  a 
small  spherical  body  lying  in  a  concave  depression  of  the  meganucleus.     Put 
the  nuclei  in  your  drawing  in  their  proper  places. 

3.  Experiments  on  Paramecium — 

a)  Formation  and  course  of  food  vacuoles:  Start  this  experiment  at  the  begin- 
ning of  the  laboratory  period,  as  it  requires  some  time  for  completion.  It  need 
not  be  watched  continuously  and  the  other  experiments  may  be  performed  during 
the  progress  of  this  one.  Mount  some  Paramecia  with  a  piece  of  scum,  add  a 
drop  of  India  ink  suspension,  and  cover.  This  experiment  can  be  carried  out 
only  on  normal  active  animals,  and  the  observations  should  be  made  on  animals 
which  are  resting  about  the  piece  of  scum.  Do  not  let  your  preparation  become 
dry.  Find  a  quiet  individual,  and  note  that  the  particles  of  carbon  are  swept 
rapidly  down  the  gullet  to  its  rounded  termination  where  they  collect  into  whirling 
spherical  masses.  Observe  that  from  time  to  time  one  of  these  masses  breaks 


PHYLUM  PROTOZOA  77 

off  and  passes  into  the  endoplasm  as  a  food  vacuole.  Observe  in  what  part  of 
the  body  the  food  vacuoles  first  collect  and  where  they  are  found  later.  Find 
out  by  observations  at  intervals  their  exact  course  in  the  endoplasm  and  make 
a  diagram  to  indicate  your  observations.  The  movement  of  the  vacuoles  is  of 
course  due  to  a  slow  circulation  of  the  endoplasm.  You  may,  if  you  watch  the 
preparation  long  enough,  be  able  to  observe  the  discharge  of  the  carbon  through 
the  anus. 

b)  Discharge  of  Jke  trichocysts:    Mount  some  Paramecia  on  a  slide,  add  a 
drop  of  picro-acetic  acid,  cover  gently,  and  examine.     Each  animal  will  be  found 
surrounded  by  a  halo  of  long  threads  which  are  the  discharged  solidified  contents 
of  the  trichocysts.     Make  a  drawing  showing  relative  lengths  of  cilia  and  the 
threads  from  the  trichocysts. 

c)  The  avoiding  reaction:  Mount  some  Paramecia  as  usual  and  observe  with 
the  low  power.     What  happens  when  the  animal  strikes  an  obstacle?    This 
reaction  is  called  the  avoiding  reaction.     Make  a  diagram  to  illustrate  the  reaction, 
showing  the  position  of  the  Paramecium  before,  during,  and  after  striking  the 
object. 

'd)  Reaction  to  chemicals:  Obtain  a  considerable  number  of  Paramecia  and 
spread  them  out  over  the  slide.  Place  the  slide  on  the  table  and  drop  a  small 
crystal  of  common  salt  in  the  center  of  the  slide.  Observe  with  the  naked  eye 
the  behavior  of  the  Paramecia  toward  the  salt.  What  does  each  Paramecium 
do  on  coming  into  the  neighborhood  of  the  salt  solution?  What  part  does  the 
avoiding  reaction  play  in  the  behavior?  Make  a  diagram  to  illustrate  the  results 
of  this  experiment. 

4.  Reproduction. — This  process  takes  place  by  division  (fission)  of  the  animal 
into  two  halves  by  a  transverse  constriction.  A  sort  of  sexual  act  called  con- 
jugation also  occurs  at  intervals,  although  it  has  been  demonstrated  that  this 
is  not  necessary  for  the  continued  existence  of  Paramecium  (Hegner,  p.  73). 

a)  Fission:  In  fission,  both  of  the  nuclei  play  an  active  r61e.  The  mega- 
nucleus  divides  by  direct  division;  the  micronucleus  by  a  very  primitive  kind 
of  mitosis,  with  the  formation  within  it  of  fibers  like  the  spindle  fibers  (see 
Hegner,  Fig.  32,  p.  70).  Study  and  draw  from  the  prepared  slides  three  stages 
of  fission,  marked  "early,"  "middle,"  and  "late."  Note  that  each  slide  contains 
only  a  few  individuals  which  are  dividing  while  the  rest  of  the  specimens  are 
merely  normal.  The  location  of  the  dividing  individuals  has  been  indicated  on 
most  of  the  slides  by  ink  marks.  Do  not  draw  until  you  are  sure  that  you  have 
found  a  specimen  in  fission. 

(i)  Early  fission:  The  beginning  of  fission  is  recognizable  by  the  elongation 
of  the  meganucleus,  which  becomes  nearly  as  long  as  the  animal.  The  micro- 
nucleus  has  moved  away  from  its  usual  position  in  a  depression  of  the  mega- 
nucleus  and  is  free  in  the  cytoplasm,  where  it  will  be  found  in  various  stages  of 
division.  It  accomplishes  this  division  by  pulling  into  two  halves  which  move 


78  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

farther  and  farther  apart  from  each  other,  drawing  out  the  connecting  band 
into  a  thinner  and  thinner  thread  which  finally  ruptures.  The  division  of  the 
micronucleus  is  completed  very  early  in  the  process  of  fission. 

(2)  Middle  fission:    The  micronucleus  is  completely  divided  and  one  of  it? 
halves  will  be  found  near  each  end  of  the  animal.    The  meganucleus  is  separat- 
ing into  two  halves  connected  by  a  slender  strand.    A  transverse  constrictioi 
is  present  across  the  center  of  the  cell. 

(3)  Late  fission:  The  division  of  the  meganucleus  has  been  completed.     The 
cytoplasmic  constriction  has  divided  the  cell  nearly  or  completely  in  two,  but 
the  two  halves  still  cling  together,     Each  half  has  regenerated  those  structures 
which  it  lacked.     The  whole  process  of  fission  requires  in  life  about  one  half  an 
hour.    The  daughter-cells  at  first  small*  *  than  the  normal  Paramecium  soon 
attain  adult  size  and  proportions. 

b)  Conjugation:  Look  over  the  slide  for  cases  in  which  two  Paramecia  are 
united  by  their  oral  grooves.  Draw.  It  is  not  practical  for  beginning  students 
to  study  the  stages  of  the  conjugation  process  but  the  texts  should  be  consulted 
for  this  information  (Hegner,  pp.  68-73). 

5.  General  considerations  on  the  Paramecium. — Is  Paramecium  more  dif- 
ferentiated than  Amoeba?  In  your  answer,  compare  in  detail  Amoeba  and 
Paramecium  as  to  definiteness  of  form,  organs  of  locomotion,  place  of  ingestion 
and  egestion  of  food,  etc.  In  what  part  of  the  protoplasm,  ectoplasm,  or  endo- 
plasm  has  the  greater  degree  of  differentiation  occurred?  Can  you  give  a  reason 
for  this?  What  does  Paramecium  gain  by  its  more  complex  structure? 

D.      GENERAL  STUDY  OF  PROTOZOAN    CULTURES 

In  order  to  obtain  Protozoa  in  abundance  it  is  necessary  to  cultivate  them  in 
a  food-containing  solution,  which  is  called  a  culture.  Such  cultures  are  made  by 
adding  boiled  grain,  hay,  bread,  pond  weeds,  etc.,  to  a  considerable  quantity  of 
water;  bacteria  from  the  air  fall  into  the  culture,  flourish  there  upon  the  food 
material  which  was  put  into  the  culture,  and  furnish  food  for  the  Protozoa, 
which  are  added  to  the  culture  from  a  natural  source,  such  as  pond  water.  Owing 
to  the  abundance  of  bacteria  in  such  artificial  cultures  the  Protozoa  increase 
by  division  until  enormous  numbers  of  them  will  be  present  in  a  relatively  small 
quantity  of  water. 

Besides  bacteria,  yeasts,  fin  J,  and  r  ^er  low  plant  forms  and  Protozoa,  small 
multicellular  animals  also  occur  in  the  cultures,  and  a  hasty  study  will  be  made 
of  them  also. 

Obtain  a  drop  or  two  of  water  from  Protozoa  cuHures  which  are  supplied; 
cover,  examine,  and  identify  as  far  as  possible  the  r  ms  present.  Sketches  of 
the  more  interesting  ones  are  desirable  if  time  pern:  &.  In  the  case  of  Protozoa 
particular  attention  should  be  paid  to  organs  of  locomotion  and  specialization? 
of  structure. 


PHYLUM  PROTOZOA  7g 

i.  Protozoa. — Learn  to  distinguish  Protozoa  from  other  microscopic  animals. 
They  are  recognizable  by  absence  of  cell  waUs  and  absence  of  organs,  their  bodies 
having  a  granular  structureless  appearance.  The  common  Protozoa  met  with 
in  cultures  besides  Paramecium  are: 

a)  Vorticella:    This  relatively  small  protozoan  is  readily  recognized  by  its 
bell-shaped  body  and  the  slender  stalk  arising  from  the  top  of  the  bell  and  per- 
manently attaching  the  animal  to  other  objects  in  the  culture.     The  stalk  is 
contractile;  in  fact  it  contains  a  spiral  muscle,  which  on  shortening  draws  the 
stalk  into  the  shape  of  a  spiral  spring.     We  thus  see  that  muscular  fibrils  can  be 
differentiated  even  within  the  limits  of  a  single  cell.     The  free  end  of  the  bell 
bears  a  circle  of  swiftly  vibrating  cilia,  and  a  large  opening  to  the  gullet.     Look 
for  food  vacuoles,  contractile  vacuoles,  e'  >.     The  horseshoe-shaped  macronucleus 
can  be  seen  only  after  staining  with  aceto-carmine. 

b)  Stentor:   This  animal  is  a  large  trumpet-shaped  form,  usually  attached 
to  objects.     The  broad  end  bears  a  circle  of  large  cilia,  and  a  conspicuous  spiral 
gullet.     The  ectosarc  is  striped.     The  stripes  are  muscular  fibrils  which  enable 
the  Stentor  to  undergo  considerable  changes  of  shape.     The  macronucleus 
resembles  a  string  of  beads  and  is  generally  a  conspicuous  object. 

c}  Eypotrichous  dilates:  This  group  of  ciliates  is  easily  distinguished  by  a 
jerky  darting  method  of  locomotion,  and  the  possession  of  large  cilia  which  are 
used  as  legs  for  creeping  over  objects.  These  cilia  are  really  fused  bundles  of 
cilia,  usually  called  cirri,  and  it  is  a  remarkable  fact  that  each  one  of  them  can 
be  moved  independently.  Look  for  gullet,  contractile  vacuole,  etc.  The 
nucleus  cannot  be  seen  without  staining.  Use  aceto-carmine.  Common  forms 
are  Euplotes,  Stylonichia,  Oxytricha. 

d)  Other  ciliates:   Ciliates  are  the  commonest  Protozoa,  and  a  great  variety 
may  be  expected  in  cultures.     Frontonia  is  similar  to  Paramecium,  but  larger 
and  more  oval  in  form;   Didinium  may  be  recognized  from  Hegner's  Fig.  26 
(p.  63) ;  Spirostomum  is  a  long,  slender,  cigar-shaped  ciliate  with  oblique  muscle 
stripes;    Lacrymaria  is  spindle-shaped  with  a  very  long,  slender,  mobile  "neck", 
Dileptus  is  a  large  form  with  a  short  contractile  neck ;  Colpoda  is  a  small  oval 
type  with  a  marked  indentation  near  the  anterior  end;    Coleps  is  distinguished 
by  an  armor  of  small  squarish  plates;    Ealteria  is  a  quite  small,  nearly  spher- 
ical ciliate,  moving  by  swift  darts.     TJ'ese  are  tl  *  forms  which  we  commonly 
get  in  cultures  "seeded"  from  natural  w     >;s  in  .  '-.e* Chicago  region,  but  many 
others  may  be  expected. 

e)  Heliozoa,  or  sun  animalcules:    Spherical  protozoans  with  stiff  radiating 
pseudopodia  and  bubbly  protoplasm  are  not  infrequently  found.     They  are 
related  to  Amoeba.     Actin*    krys,  small,  and  Actinosphaerium,  quite  large,  are 
the  common  kinds. 

/)  Amoeboid  organisms:    The   only   other   common  protozoan,   similar   to 
Amoeba,  is  Arcella.     This  animal  resembles  Amoeba  in  all  essential  respects 


8o  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

except  that  it  secretes  a  brown  hemispherical  shell  in  which  it  lives  and  which 
it  carries  on  its  back,  so  to  speak,  when  it  moves  about.  It  is  relatively  common 
in  cultures. 

g)  Flagellates:  Organisms  similar  in  appearance  to  the  Euglena  figured  and 
described  in  Hegner  (p.  82)  are  not  uncommon  in  cultures.  Some  are  green, 
some  colorless,  all  possess  long  threadlike  flagella  as  locomotor  organs,  although 
these  are  often  very  difficult  to  see,  as  they  are  transparent.  Flagellates  are 
best  recognized  by  a  peculiar  swaying  type  of  swimming  movement,  quite 
distinct  from  the  movement  of  ciliates. 

2.  Multicellular  organisms. — These  are  readily  distinguishable  from  Protozoa 
by  the  presence  of  definite  organs  in  their  bodies.  See  Hegner  (pp.  5-6)  for 
the  general  characters  of  the  different  phyla.  One  usually  finds  in  cultures  the 
following  types: 

a)  The   rotifers,    or   wheel    animalcules    (Phylum    Trochelminthes) :    These 
extremely  common  animals  are  at  once  known  by  the  presence  of  one  or  two 
disks  of  cilia  on  their  anterior  ends.     The  constant  movement  of  these  cilia 
produces  the  illusion  of  a  rotating  wheel.     The  ciliary  apparatus  can  be  folded 
into  the  head.     Other  interesting  features  are  the  internal  jaws,  which  keep  up 
a  constant  chewing  movement,  the  jointed  telescopic  posterior  end,  often  pro- 
vided with  one  or  more  "toes"  for  clinging  to  objects,  and  the  hard  case,  or 
lorica,  which  often  incloses  the  animal.     The  most  common  rotifer  in  cultures 
is  Philodina,  which  possesses  a  pair  of  "wheels." 

b)  Roundworms  or  nematodes  (Phylum  Nemathelminthes),  slender,  cylindrical, 
wormlike  animals,  pointed  at  both  ends,  without  cilia,  moving  by  violent  alternate 
curving  and  straightening  of  the  body. 

c)  Flatworms  (Phylum  Platyhelminthes) ,  slender  flattened  animals,  moving 
in  a  smooth  gliding  manner,  due  to  the  presence  of  cilia;    with  more  or  less 
definite  heads.     Stenostomum  is  the  commonest  form,  and  often  occurs  in  chains, 
produced  by  fission. 

d)  Chaetonotus  (Phylum  Trochelminthes?):    This  animal,  possibly  related 
to  the  rotifers,  resembles  a  ciliate  protozoan.     It  has  a  slender  flexible  body, 
possessing  in  front  a  rounded  head  region,  followed  by  a  short  "neck,"  and  at  the 
posterior  end  two  pointed  processes.     The  whole  surface  is  covered  with  short 
spines. 

e)  Naids   (Phylum  Annelida),  slender  cylindrical  worms,  provided  with 
projecting  bristles  at  regular  intervals.     The  smallest  ones  belong  to  the  genus 
Aeolosoma,  and  have  beautiful  red,  orange,  or  green  spots.     Some  (Stylaria, 
Pristina)  have  a  long,  slender,  very  active  proboscis  at  the  anterior  end.    Dero 
is  provided  at  the  posterior  end  with  an  expansible  hood  bearing  several  ciliated 
gills.     Most  of  the  naids  are  quite  large  compared  to  the  other  forms  we  have 
been  describing.     They  also  occur  in  chains  produced  by  fission. 


PHYLUM  PROTOZOA  81 

/)  Water  mites  and  water  bears  (Phylum  Arthropoda):  These  are  round  to 
oval  flat  animals  with  projecting  legs.  The  water  mites  have  six  jointed  legs 
in  the  young  state,  eight  in  the  adult.  The  water  bear  has  eight  short,  non- 
jointed  legs  provided  with  claws. 

g)  Entomostraca  (Phylum  Arthropoda) :  These  common  animals  have 
conspicuous  jointed  legs,  and  often  large  jointed  antennae  projecting  from  the 
head.  They  swim  in  a  jerky  manner.  One  of  the  commonest  types  is  Cyclops, 
a  small  animal  with  a  jointed  body,  single  median  eye,  long  swimming  antennae, 
and  slender  terminal  spines;  often  also  with  two  sacs  full  of  eggs  hanging  to 
the  body.  The  water  fleas  have  well-marked  heads  with  large  eyes,  and  powerful 
swimming  antennae,  but  the  body  is  inclosed  in  a  double  shell,  from  which  the 
jointed  legs  may  be  protruded  from  time  to  time. 

This  brief  account  of  the  microscopic  animals  commonly  found  in  pond  water 
is  merely  intended  to  give  the  student  an  idea  of  the  variety  of  form  and  structure 
of  aquatic  life.  Students  who  are  interested  will  find  more  detailed  accounts 
of  these  animals  in  Stokes's  Aquatic  Microscopy,  obtainable  in  the  library. 


X.    PHYLUM  COELENTERATA 

A.      HYDRA 

i.  General  structure. — Note  the  appearance  of  the  animals  in  the  culture. 
They  are  sessile,  that  is,  attached  to  the  glass,  plants,  etc.,  by  one  end  while 
the  rest  of  the  body  hangs  free  in  the  water.  Obtain  a  living  Hydra  and  place 
in  a  watch  glass  with  sufficient  water  to  cover  the  animal.  Examine  with  the 
lowest  power  of  the  microscope  or  with  a  hand  lens,  and  note  the  following 
parts  (Hegner,  chap,  viii,  pp.  116-38). 

The  body  or  column  of  the  animal  is  a  cylindrical  elastic  tube,  capable  of 
great  extension  and  contraction.  From  one  end  of  this,  which  is  the  oral, 
anterior,  or  distal  end,  arise  a  number  of  radially  arranged  slender  outgrowths, 
the  tentacles.  The  number  of  these  varies  from  four  to  ten,  but  is  generally  five 
or  six.  The  oral  extremity  between  the  bases  of  the  tentacles  forms  a  conical 
elevation,  the  hypostome,  in  the  center  of  which  the  mouth  is  located.  The 
mouth  when  closed  has  a  star-shaped  appearance  but  is  usually  difficult  to  see, 
unless  the  hypostome  happens  to  be  turned  directly  upward.  The  flattened 
base  of  the  animal  is  the  posterior,  aboral,  or  proximal  end,  is  often  designated 
as  the  foot  or  basal  disk,  and  secretes  a  cement-like  substance  by  which  the 
organism  attaches  itself.  Column  and  tentacles  are  hollow,  inclosing  a  cavity 
known  as  the  gastrovascular  cavity  because  it  has  both  digestive  and  circulatory 
functions.  Under  the  low  power  the  gastrovascular  cavity  appears  outlined  by 
brownish  lines  in  most  specimens;  it  is  usually  an  extensive  cavity  only  in  the 
anterior  half  of  the  column,  being  reduced  posteriorly  to  a  slender  canal. 

Observe  the  tentacles  more  closely  and  note  that  they  bear  numerous  pro- 
tuberances, each  of  which  contains  a  collection  of  very  small  oval  sharply  out- 
lined bodies,  the  stinging  cells  or  nematocysts.  Such  a  collection  of  stinging  cells 
is  called  a  battery.  At  the  end  of  each  tentacle  is  a  great  mass  of  stinging 
cells.  They  also  occur  sparingly  on  the  column. 

Hydra  is  not  bilaterally  symmetrical,  like  the  frog,  where  there  is  only  one 
possible  plane  that  will  divide  the  animal  into  similar  halves,  but  is  radially 
symmetrical,  that  is  the  parts  of  the  body  radiate  from  a  common  axis  so  that 
a  number  of  planes  of  symmetry  could  be  passed  through  the  animal.  How  do 
you  think  the  differentiation  and  development  of  the  anterior  end  compare 
with  that  of  the  frog?  Does  it  seem  to  have  any  special  structures  different 
from  the  rest  of  the  body? 

Draw  a  Hydra  in  the  extended  state  showing  the  above-mentioned 
details. 

82 


PHYLUM  COELENTERATA  83 

2.  General  behavior  (Hegner,  pp.  127-33).— On  your  own  specimen  or  on 
those  in  the  general  culture  jar  perform  the  following  simple  experiments.     Use 
a  dean  needle,  touch  the  animals  gently,  and  wait  for  the  animal  to  expand 
completely  before  stimulating  it  again  or  use  a  different  specimen.     Touch  one 
tentacle  of  a  fully  expanded  individual  gently.    Does  it  contract?    Do  other 
parts  contract?     Touch  two  or  three  tentacles  simultaneously.     Is  the  response 
more  marked  than  before?     Try  the  comparative  effect  of  a  touch  of  the  same 
intensity  on  the  foot,  middle  of  the  column,  and  hypostome.    What  parts  of  the 
animal  are  the  most  sensitive?   least  sensitive?    Try  difference  in  response  to 
a  weak  and  strong  stimulus  applied  to  the  same  region.     Stir  the  water  in  the 
culture  and  observe  what  happens.     Do  any  of  these  experiments  indicate  that 
the  stimulus  is  conducted  from  the  point  of  stimulation  to  other  parts,  as  in  the 
frog?    As  in  the  frog  the  mechanism  of  irritability  and  perception  of  stimuli 
is  a  nervous  system  and  sensory  cells  and  the  mechanism  of  response  consists 
of  muscle  fibers.     Owing,  however,  to  the  very  simple  structure  of  these  systems, 
there  is  but  one  response  to  all  kinds  of  stimuli,  namely,  contraction. 

Make  an  outline  drawing  of  a  fully  contracted  Hydra. 

3.  Cellular  structure  of  the  living  animal. — Mount  a  Hydra  on  a  slide  and 
support  the  cover  glass  with  small  bits  of  broken  glass  or  slivers  of  wood  so  that 
the  animal  will  not  be  crushed.     The  support  must  be  thick  enough  to  allow  the 
animal  to  extend  itself  freely  under  the  cover  glass  but  not  so  thick  as  to  interfere 
with  the  use  of  the  high  power.     Small  individuals  are  best  for  the  purpose. 

a)  Cellular  structure  of  the  column:  The  animal  must  be  fully  extended  for 
the  following  observations.     Hydra  consists  of  two  layers  of  cells,  an  outer 
ectoderm  and  an  inner  entoderm  with  a  structureless  gelatinous  sheet,  the  meso- 
gloea,  between  them.    It  is  thus  like  two  closely  fitting  cylinders,  one  within 
the  other.     Hydra  is  therefore  a  diploUastic  animal,  that  is,  it  consists  of  two 
germ  layers  (Hegner,  p.  no).     Examine  the  base  of  the  column  near  the  foot 
with  the  high  power  and  try  to  see  these  two  layers.     First  focus  on  the  surface 
of  the  column  and  observe  that  it  consists  of  a  mosaic  of  elongated  cells,  with 
pointed  ends.     These  are  called  the  epithelio-muscular  cells  of  the  ectoderm 
because  each  has  an  epithelial  and  a  muscular  portion.    A  few  nematocysts,  oval 
distinct  bodies,  also  occur  lying  in  the  ectoderm  cells,  and  there  may  sometimes 
be  observed  between  some  of  the  epithelio-muscular  cells  greenish  groups  of 
very  small  cells,  the  interstitial  cells.     Now  focus  slowly  downward,  and  a  new 
layer  of  larger,  more  rounded,  clear  cells,  the  nutritive  muscular  cells  of  the  ento- 
derm, comes  into  view.     Focus  on  the  edge  of  the  animal;   the  ectoderm  then 
appears  in  profile  as  a  rather  thin  layer,  separated  from  the  thicker  entoderm 
by  a  dark  line  of  uniform  width,  the  mesogloea. 

b)  Cellular  structure  of  the  tentacle:    Examine  the  base  of  a  fully  extended 
tentacle,  and  repeating  the  above-mentioned  procedure  observe  first  the  ectoderm 
cells;    then  by  focusing  on  the  optical  center  note  the  large  clear  rectangular 


84  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

or  cuboidal  entoderm  cells,  the  line  of  mesogloea,  and  the  profile  view  of  the 
ectoderm.  The  center  of  the  tentacle  is  occupied  by  a  slender  canal,  a  branch 
of  the  gastrovascular  system,  but  this  is  distinctly  identifiable  only  when  food 
particles  in  it  can  be  seen  moving  back  and  forth.  Draw  a  small  portion  to 
show  the  cell  arrangement  in  optical  section.  Then  examine  the  more  distal 
(i.e.,  farther  away  from  the  body)  portions  of  the  tentacle  to  see  the  arrangement 
of  the  stinging  cells.  Each  group  of  stinging  cells,  or  battery,  is  contained 
within  a  single  ectoderm  cell,  and  causes  a  conical  projection  which  appears 
clearly  when  the  ectoderm  is  viewed  in  profile.  Note  the  definite  arrangement 
of  large  and  small  nematocysts  in  each  battery  and  the  projecting  spines,  the 
cnidocils,  best  seen  in  profile.  Draw  a  small  portion  of  the  tentacle  to  show 
several  batteries. 

4.  The  nematocysts. — Remove  the  supports  from  under  the  cover  glass 
and  drum  on  the  cover  glass  with  the  point  of  a  pencil  until  the  animal  is  thor- 
oughly crushed.     This   discharges   the  nematocysts.    With   the  high   power 
examine  undischarged  and  discharged  nematocysts.     There  are  usually  three 
kinds  of  them,  a  large  barbed  and  two  small  non-barbed  varieties. 

a)  Large  barbed  nematocysts:  In  the  undischarged  state  these  are  oval  sacs, 
with  one  end  flattened.     From  the  flat  end  a  hollow  pouch  projects  into  the 
interior,  and  from  the  inner  end  of  this  a  coiled  thread  arises  filling  the  rounded 
part  of  the  sac.    When  discharged,  pouch  and  thread  are  projected  to  the  exterior, 
turning  inside  out.    The  pouch  bears  three  large  spikes  and  some  quite  small 
ones  (see  Hegner,  Fig.  56,  p.  121).     Some  kinds  of  Hydras  have  two  sizes  of  this 
type  of  nematocyst. 

b)  Small  oval  nematocysts:  These  are  much  smaller  than  the  preceding,  oval 
or  cylindrical,  generally  pointed  at  one  end.     When  undischarged  a  spirally 
coiled  thread  fills  the  whole  interior,  projecting  inward  from  the  pointed  end. 
When  discharged  the  extremely  long  fine  thread  readily  identifies  this  type. 

c)  Small  spherical  nematocysts:  These  are  a  little  smaller  than  the  preceding 
and  more  spherical.     Each  contains  a  thick  thread  which  makes  a  single  loop, 
inside  the  nematocyst  and  fojrns  a  tight  little  coil  of  three  or  four  turns  when 
discharged  (see  Hegner,  Fig.  57,  p.  122). 

Nematocysts  are  not  really  cells  but  cell  products  secreted  by  the  interstitial 
ceUs,  which  may  frequently  be  seen  clinging  to  them.  Interstitial  cells  engaged 
in  forming  nematocysts  are  called  cnidoblasts,  and  from  them  project  slender 
spines,  the  cnidocils,  whose  stimulation  is  supposed  to  cause  the  explosion  of  the 
nematocysts. 

Draw  as  many  kinds  of  discharged  and  undischarged  nematocysts  as  you 
can  find  without  spending  too  much  time  upon  them. 

5.  Cellular  structure  from  slides. — 

a)  Longitudinal  section:  Examine  slide  "  Hydra — long."  Find  a  nearly 
median  longitudinal  section.  Identify  under  low  power  the  ectoderm,  with 


PHYLUM  COELENTERATA  85 

its  numerous  darkly  stained  nematocysts,  the  line  of  mesogloea,  and  the  elongated 
irregular  highly  vacuolated  entoderm  cells.  In  the  region  of  the  hypos  tome 
note  the  granular  appearance  of  the  entoderm,  indicating  glandular  functions,  as 
it  here  secretes  mucus  to  aid  in  swallowing  food;  observe  also  the  folds  in  this 
region,  permitting  great  distension  of  the  mouth.  On  some  of  the  sections  the 
continuation  of  the  gastrovascular  cavity  into  the  tentacles  can  probably  be 
observed.  Make  a  low-power  diagrammatic  drawing  of  the  section,  constructing 
it  from  what  you  have  seen  on  several  sections. 

b)   Cross-section:    Examine  slide  "  Hydra — trans."     Make  a  careful  study 
with  the  high  power  of  the  cell  structure. 

(1)  Ectoderm:  The  ectoderm  consists  of  a  sheet  of  cells  one  cell  thick,  form- 
ing a  continuous  outer  layer  of  the  animal,  and  appearing  as  the  outer  circle  in 
the  cross-section.     It  is  composed  mainly  of  large  epithelio-muscular  cells  whose 
boundaries  are  often  indistinct.     The  greater  part  of  each  of  these  cells  is  a 
polyhedral  epithelial  cell,  but  the  base  is  drawn  out  into  a  long,  slender,  muscular 
fibril,  running  in  a  longitudinal  direction.     Thus  the  bases  of  all  the  ectoderm 
cells  produce  a  longitudinal  muscle  coat  for  the  Hydra,  by  means  of  which  it  is 
able  to  contract.     (For  the  appearance  of  the  muscle  fibrils  see  below  under 
"Mesogloea.")    Each  epithelio-muscular  cell  has  a  large  nucleus,  easily  recognized 
by  its  black  central  nucleolus  and  distinct  network.     Within  many  of  the 
epithelio-muscular  cells  are  numerous  darkly  stained  nematocysts,  of  which  the 
various  types  described  above  will  be  recognized.     Each  is  inclosed  in  its  mother- 
cell,  the  cnidoblast,  which  is  a  modified  interstitial  cell.    These  latter  are  small, 
dark,  granular  cells,  each  about  the  size  of  a  nucleus  of  the  ordinary  ectoderm 
cells,  and  occurring  in  groups  or  masses  which  are  within  or  between  the  epithelio- 
muscular  cells. 

(2)  Entoderm:    The  entoderm  like  the  ectoderm  is  a  continuous  sheet  of 
cells,  forming  a  sort  of  inner  tube  for  the  animal.     It  is  made  up  chiefly  of  the 
nutritive  muscular  cells,  or  digestive  cells,  large,  elongated,  vacuolated  cells,  with 
well-defined  walls,  and  bulbous,  crowded  inner  ends.     They  usually  contain  many 
food  particles  and  droplets,  have  a  nucleus  like  that  of  the  ectoderm  cells  and  a 
small  amount  of  granular  cytoplasm,  confined  mainly  to  the  inner  ends.     Their 
outer  ends,  next  to  the  mesogloea,  are  also  prolonged  into  muscular  fibrils,  which 
run  circularly,  forming  a  circular  coat,  but  this  is  relatively  poorly  developed  as 
compared  with  the  outer  longitudinal  coat.    Situated  between  the  inner  ends  of  the 
digestive  cells  is  another  type  of  cell,  the  secretory  or  glandular  cell,  which  produces 
the  digestive  enzymes.     This  appears  as  a  small  triangular  cell,  filled  with  a 
network,  resting  between  the  diverging  inner  ends  of  the  adjacent  nutritive  cells. 

(3)  Mesogloea:  The  mesogloea  is  not  a  cell  layer  but  a  sheet  of  gelatinous 
material  cementing  the  ectoderm  and  entoderm  together.     The  longitudinally 
directed  muscular  bases  of  the  ectoderm  cells  are  imbedded  in  the  mesogloea  and 
appear  there  as  dark  dots. 


86  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

Draw  a  small  portion  of  the  section  in  great  detail  to  show  all  the  kinds  of 
cells  present. 

6.  Reproduction. —  Hydra  reproduces  by  the  asexual  process  of  budding  or 
by  the  reproduction  of  eggs  and  sperm  in  definite  reproductive  organs.     Living 
material  with  sex  organs  is  available  only  in  the  autumn. 

a)  Budding:    If  living  specimens  with  buds  are  available  obtain  one  and 
make  a  simple  outline  drawing. 

b)  Male  reproductive  organs:    Examine  slide  at  demonstration  microscope. 
The  male  organs,  spermaries  or  testes,  form  conical  elevations  in  the  ectoderm 
each  provided  with  a  nipple-like  extension  for  the  exit  of  the  sperm.     Draw. 

c)  Female  reproductive  organs:  Demonstration  slide.     The  ovaries  are  located 
nearer  the  aboral  end  than  the  testes,  form  low  broad  elevations,  and  lack  the 
nipple.    Each  contains  a  single  (or  sometimes  two)  large  amoeboid  ovum.    Draw. 

7.  General  considerations  on  Hydra. — The  chief  differences  that  we  may 
note  between  Hydra  and  the  Protozoa  is  that  it  consists  of  several  different  kinds 
of  cells,  each  with  specific  functions,  and  that  these  cells  are  arranged  in  definite 
layers,  which  foreshadow  the  systems  and  organs  of  the  higher  animals.     To 
what  stage  of  the  embryonic  development  of  the  frog  does  the  Hydra  correspond? 
Which  of  its  two  layers  is  the  more  differentiated  and  what  reason  can  you  give 
for  this?    In  Hydra,  digestive,  muscular,  reproductive,  and  nervous  (see  Hegner, 
p.   125)  systems  are  present,  at  least  in  a  simple  condition.     What  systems 
which  the  frog  has  are  totally  lacking  in  the  Hydra  and  how  does  it  accomplish 
the  functions  performed  by  those  systems  when  they  are  present?     In  what 
way  is  the  process  of  digestion  in  Hydra  like  that  of  the  frog  and  in  what  way 
like  that  of  the  Protozoa  (Hegner,  p.  127)? 

We  may  further  notice  that  the  Hydra  is  not  merely  a  collection  of  many 
cells  of  several  different  kinds  but  that  these  cells  act  together  for  the  general 
welfare  of  the  animal,  and  each  one  is  more  or  less  helpless  without  the  others, 
since  it  has  become  specialized  for  particular  functions,  and  hence  cannot  success- 
fully perform  all  functions  like  a  protozoan  cell.  Hydra  is  therefore  an  individual, 
a  unity  produced  by  co-operation,  ruled  by  a  dominant  region,  the  anterior  end 
or  head,  which,  to  be  sure,  is  as  yet  not  very  distinctly  differentiated  from  the 
rest  of  the  body. 


B.      A   COLONIAL   COELENTERATE 

For  this  study  either  Obelia  or  Campanularia  may  be  used.  As  these  animals 
live  in  the  ocean,  only  preserved  material  can  be  obtained.  Obtain  a  preserved 
colony  and  examine  in  a  watch  glass  of  water  (Hegner,  pp.  139-40). 

i.  General  structure. — The  coelenterate  forms  a  branching  colony  of  plant- 
like  appearance  consisting  of  a  number  of  individuals,  each  of  which  is  similar 
to  a  Hydra.  Identify  the  rootlike  basal  branches,  the  hydrorhiza,  by  means  of 


PHYLUM  COELENTERATA  87 

which  the  colony  is  attached  to  solid  objects,  the  main  stem,  or  hydrocaulus, 
and  the  branches,  each  one  of  which  terminates  in  an  individual  which  bears  a 
general  resemblance  to  Hydra,  and  is  called  a  zooid,  hydranth,  or  polyp.  The 
whole  colony  is  spoken  of  as  a  hydroid  colony.  The  zooids  are  produced  by 
budding  from  the  stems,  just  as  in  Hydra.  In  fact  if  the  buds  of  Hydra  should 
remain  attached  to  the  parent  a  hydroid  colony  would  be  produced.  Make  a 
small  sketch  to  show  the  general  appearance  of  the  colony. 

2.  Detailed  structure. — Mount  some  of  the  preserved  material  on  a  slide 
or  examine  the  slide  of  a  hydroid  in  your  box.  Use  the  low  power.  The  hydro- 
caulus and  branches  are  covered  by  a  horny  layer,  the  perisarc,  which  they  secrete. 
The  perisarc  extends  up  around  each  of  the  zooids  in  the  form  of  a  wineglass, 
the  hydrotheca.  At  the  base  of  each  branch  the  perisarc  is  ringed,  probably  to 
make  the  stem  more  flexible.  Within  the  perisarc  is  the  coenosarc,  a  hollow  tube 
comparable  to  the  column  of  Hydra  and  consisting,  like  the  latter,  of  ectoderm, 
endoderm,  and  mesogloea.  Its  cavity  is  the  gastrovascular  cavity  and  is  con- 
tinuous throughout  the  colony.  There  are  two  kinds  of  zooids. 

a)  Nutritive  zooids:   This  is  the  more  abundant  kind  of  zooid.     It  consists 
of  a  cylindrical  body  from  which  arises  the  club-shaped  manubrium,  terminating 
in  the  wide  mouth  opening.     At  the  base  of  the  manubrium  is  a  circlet  of  tentacles 
bearing  nematocysts.     The  hydrotheca  has  a  sort  of  shelftike  extension  inward 
at  the  point  where  the  body  of  the  zooid  continues  into  the  coenosarc.     Draw  a 
nutritive  zooid. 

b)  Gonozooids:    These  modified  zooids  will  be  found  where  the  branches 
arise  from  the  hydrocaulus.     Each  is  surrounded  by  a  cylindrical  case  of  perisarc, 
called  the  gonotheca,  open  at  the  end.     The  gonozooid  consists  of  a  central  stalk 
or  blastostyle,  which  is  a  degenerate  nutritive  zooid,  and  a  number  of  saucer- 
shaped  bodies  borne  upon  the  blastostyle  and  almost  concealing  it  from  view. 
The  saucer-shaped  bodies  are  medusa  buds.     They  are  formed  by  a  process  of 
budding  from  the  blastostyle,  and  eventually  they  become  free,  escape  from  the 
gonotheca,  and  swim  about  in  the  water  as  little  bell-shaped  animals,  called 
medusae.    The  medusa  is  the  sexual  individual  and  gives  rise  to  eggs  or  sperms 
(on  separate  medusae) ;  the  fertilized  egg  develops  into  a  new  colony.    Have  the 
assistant  show  you  a  medusa.     Draw  a  gonozooid. 

In  these  colonial  coelenterates  there  exist  then  three  kinds  of  individuals: 
the  nutritive  zooid,  whose  function  is  that  of  food  getting;  the  gonozooid,  whose 
function  is  to  bud  off  medusae;  and  the  medusa,  whose  function  is  reproduction. 
Such  a  condition  is  known  as  polymorphism,  or  division  of  labor,  because  the 
organism  instead  of  differentiating  into  organs  for  the  performance  of  different 
functions,  as  the  frog  does  (which  its  simple  structure  does  not  indeed  permit) , 
differentiates  into  several  kinds  of  individuals  for  the  performance  of  various 
functions.  The  hydroids  also  illustrate  the  principle  of  metagenesis,  or  alterna- 
tion of  generations  (Hegner,  p.  141),  that  is,  the  medusa  or  sexual  generation  is 


88  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

conceived  of  as  alternating  with  the  hydroid  colony,  or  asexual  generation. 
It  would  probably  be  advisable  to  drop  this  idea  altogether  and  to  regard  the 
medusa  simply  as  the  final  or  adult  stage  in  the  development  of  the  organism. 


C.   GENERAL  SURVEY  OF  OTHER  COELENTERATES 

Study  the  collection  of  coelenterates  provided  for  the  class,  reading  what 
Hegner  has  to  say  about  them  (pp.  139-43).  Acquaint  yourself  with  the  general 
appearance  of  the  following  chief  groups  of  coelenterates: 

1.  The  hydroids. — These  animals  are  extremely  common  along  the  shores 
of  the  ocean,  forming  beautiful  plantlike  growths  on  rocks,  wharves,  plants, 
shells  of  animals,  etc.     Note  various  types  of  branching,  size  and  shape  of 
zooids,  etc. 

2.  Medusae. — Medusae,  as  stated  above,  are  the  sexual  stage  of  the  hydroid 
colonies.     They  are  small,  gelatinous,  bell-shaped  animals  with  tentacles  hanging 
free  from  the  edge  of  the  bell  and  a  mouth  dependent  from  the  center  of  the 
concave  surface  of  the  bell.     From  the  mouth,  canals  (usually  four)  radiate  to 
the  periphery  of  the  bell  and  serve  as  a  food-distributing  system.     A  circular 
muscular  shelf,  the  velum,  extends  inward  from  the  edge  of  the  bell;  its  contrac- 
tions enable  the  animal  to  swim.    Tlie  jelly-like  composition  of  the  medusae  is 
due  to  the  enormous  development  of  the  mesogloea. 

3.  True  jellyfishes. — These  differ  from  the  medusae,  which  are  also  often 
called  jellyfishes,  through  the  absence  of  a  velum,  larger  size  and  more  saucer- 
like  form,  and  more  complicated  structure.     They  usually  do  not  pass  through 
a  hydroid  stage. 

4.  Siphonophora. — These  strange  free-floating  hydroid  colonies  illustrate  the 
principle  of  division  of  labor  carried  to  its  highest  development,  since  they  may 
consist  of  seven  or  eight  different  types  of  individuals.     The  famous  Physalia, 
or  Portuguese  man-of-war  has  a  large  "float"  (which  is  a  modified  medusa),  from 
the  lower  side  of  which  the  other  members  of  the  colony  hang  down,  with  long 
trailing  tentacles.     The    Velella,  or  purple  sail,  has  a  flattened  disklike  float 
bearing  an  erect  "sail,"  with  zooids  on  the  under  surface  of  the  float.     In  other 
types  of  Siphonophora  the  float  is  lacking  but  the  upper  part  of  the  colony 
consists  of  a  circle  or  a  long  chain  of  swimming  bells,  which  are  modified  medusae. 

5.  Sea  anemones. — These  beautiful  animals  of  the  seashore  are  similar  in 
appearance  to  hydroid  polyps,  but  their  internal  structure  is  somewhat  more 
complicated  and  they  have  no  medusa  stage.    They  have  a  stout  column  with 
an  oral  disk  covered  with  tentacles. 

6.  Stony  corals. — The  common  corals  which  build  up  the  keys  and  reefs  are 
small  animals  of  the  same  structure  as  sea  anemones.     They  secrete  an  external 
skeleton  of  calcium  carbonate,  which  persists  after  they  perish.     In  all  dry  speci- 
mens of  coral  the  animals  are  of  course  destroyed,  but  the  cuplike  depressions 


PHYLUM  COELENTERATA  89 

which  they  occupy  in  life  are  readily  recognizable.  When  the  cups  are  incom- 
plete laterally,  so  as  to  be  fused  into  long  furrows,  the  familiar  "  brain'*  corals 
result. 

7.  The  horny  corals  and  their  relatives  include  the  coral  used  in  jewelry,  the 
organ-pipe  coral,  and  other  forms.     The  animals  which  secrete  these  skeletons 
have  eight  feathery  tentacles. 

8.  The  sea  feathers,  sea  fans,  etc. — These  plantlike  horny  skeletons  are  built 
up  by  minute  zooids,  which  occupy  the  small  holes  which  will  be  found  on  closer 
inspection  distributed  abundantly  over  the  skeletons. 


XI.     PHYLUM  PLATYHELMINTHES 

A.      PLANARIA 

1.  General  appearance  and  behavior. — Obtain  one  of  the  living  animals  in 
a  watch  glass  and  examine  with  a  hand  lens  (Hegner,  pp.  153-58).     Compare 
form,  symmetry,  and  arrangement  of  parts  with  that  of  Hydra  and  the  frog. 
Which  of  these  two  animals  does  it  most  resemble?    What  type  of  symmetry 
does  it  possess?    Does  it  have  anterior  and  posterior  ends?  dorsal  and  ventral 
surfaces?    Is  the  head  better  differentiated  than  in  Hydra?    On  the  dorsal 
surface  of  the  head  is  placed  a  pair  of  eyes,  and  each  side  of  the  head  is  extended 
into  a  blunt  contractile  lobe,  or  auricle. 

Observe  the  peculiar  gliding  form  of  locomotion.  To  what  is  it  due  (^4)? 
Does  the  animal  exhibit  muscular  movements  also?  Do  these  suggest  a  better 
developed  muscular  system  than  is  present  in  Hydra?  How  do  the  anterior 
end  and  auricles  behave  during  locomotion?  What  does  this  suggest  as  to  their 
function?  Touch  various  parts  of  the  animal  with  a  needle  and  note  its  behavior 
and  relative  sensitivity  of  different  regions.  Do  you  think  that  Planaria  is  able  to 
respond  more  effectively  to  stimuli  and  in  a  greater  variety  of  ways  than  Hydra  ? 

Make  an  accurate  outline  drawing  several  inches  long  of  the  animal. 

2.  Detailed  structure. — Place  a  small  Planaria  on  a  slide  and  anaesthetize 
with  a  few  grains  of  chloretone  04).     After  it  has  become  motionless,  turn  it 
ventral  surface  up  and  cover  with  a  cover  glass,  pressing  gently  so  as  to  flatten 
the  animal.     If  a  cover  glass  is  not  heavy  enough,  use  a  piece  of  thin  slide.     The 
animal  must  not  be  crushed.     Examine  under  the  low  power  of  the  microscope. 

a)  General  regions  and  surface  of  the  body:   The  narrow  clear  border  of  the 
animal  is  the  ectoderm,  the  central  branching  dark  brown  or  gray  material  is  the 
entoderm,  and  the  lighter  brown  material  between  these  two  is  the  mesoderm. 
Focus  on  the  surface  of  the  body  and  note  the  numerous  minute  pigment  granules 
which  give  the  animal  its  dark  color.     Focus  on  the  ectoderm  with  the  high  power, 
and  observe  the  numerous  rodlike  bodies,  placed  at  right  angles  to  the  surface, 
which  it  contains.     These  are  called  rhabdites,  and  when  discharged  on  the 
surface  they  soften  to  produce  mucus.     The  ectoderm  is  clothed  with  cilia, 
particularly  on  the  ventral  surface,  and  these  may  be  seen  by  focusing  on  the 
edge  of  the  ectoderm. 

b)  Sense  organs  of  the  head:   Examine  an  eye.     It  consists  of  a  clear  area, 
where  the  sensory  cells  are  located,  and  a  crescent-shaped  mass  of  very  black, 
closely  packed  granules,  whose  function  apparently  is  to  concentrate  the  light 
upon  the  sensory  cells  by,  preventing  reflection  and  diffusion.     As  the  eye  of 

90 


PHYLUM  PLATYHELMINTHES  91 

Planaria  has  no  lens  it  cannot  perceive  objects  but  can  only  distinguish  different 
degrees  of  intensity  of  light.  The  general  body  surface  of  Planaria  is  also 
sensitive  to  light  but  less  so  than  the  eyes.  The  pointed  tip  of  the  head  and  the 
auricles  appear  lighter  in  color  than  the  rest  of  the  body.  They  are  important 
sensory  areas,  containing  a  variety  of  sensory  cells,  principally  for  contact  and 
chemical  sense,  the  latter  essential  to  the  detection  of  food. 

c)  The  digestive  system:  In  the  center  of  the  body  is  an  oval  clear  region,  the 
pharyngeal   chamber,  in  which  is  located  a  cylindrical   contractile  tube,  the 
pharynx.   The  pharynx  is  attached  at  its  anterior  end  to  the  wall  of  the  pharyngeal 
chamber,  and  its  free  posterior  end  has  a  wide  opening.     The  pharyngeal  cham- 
ber opens  on  the  ventral  surface  by  the  mouth,  which  appears  as  a  small  circular 
clear  area,  devoid  of  granules,  situated  in  the  median  line  anterior  to  the  posterior 
end  of  the  pharynx.    When  the  animal  feeds,  the  free  end  of  the  elastic  pharynx 
is  protruded  as  a  proboscis  through  the  mouth.     The  student  should  understand 
clearly  the  relations  of  mouth,  pharynx,  and  pharyngeal  chamber  and  have  the 
assistant  make  further  explanations,  if  necessary. 

At  its  anterior  end  the  pharynx  opens  into  the  intestine  or  digestive  tract 
proper  (the  pharynx  being  really  an  outgrowth  of  the  body  wall),  which  divides 
at  once  into  three  main  branches,  a  median  anterior  branch  extending  forward 
as  far  as  or  between  the  eyes,  and  two  posterior  branches  which  pass  backward, 
one  on  each  side  of  the  pharyngeal  chamber,  to  the  posterior  end.  Each  main 
branch  gives  off  numerous  side  branches  or  diverticula,  often  very  irregular  in 
form,  and  these  may  make  secondary  fusions  to  form  further  longitudinal 
branches.  The  digestive  tract  generally  appears  gray  or  brown  and  is  easily 
seen  if  the  animal  is  well  pressed  out  and  more  than  the  usual  amount  of  light 
admitted  through  the  diaphragm. 

Add  to  your  outline  drawing  these  details  of  structure. 

The  digestive  canal  of  Planaria,  although  commonly  called  intestine,  differs 
from  the  true  intestines  of  the  higher  animals  in  that  it  consists  of  a  single  layer 
of  cells,  the  entoderm,  and  is  not  separated  from  the  other  structures  of  the  body 
as  a  definite  tube.  It  is  in  reality  much  more  comparable  to  the  wall  of  the 
gastrovascular  cavity  of  Hydra  and  its  cavity  corresponds  completely  to  this 
cavity  in  Hydra,  except  that  it  is  more  branched  and  hence  more  effective  as  a 
food-distributing  system. 

d)  Other  systems  of  Planaria:  The  animal  has  well-differentiated  nervous, 
excretory,  and  reproductive  systems,  but  unfortunately  these  are  difficult  or 
impossible  to  study.     Read  carefully  Hegner's  description  of  them  (pp.  155-57). 
In  the  nervous  system  note  especially  the  concentration  of  nervous  tissue  in  the 
head  between  the  eyes,  constituting  the  beginning  of  a  brain.     The  structure 
of  the  excretory  system  should  also  be  carefully  studied,  as  it  is  constructed  upon 
a  primitive  plan  from  which  the  excretory  systems  of  nearly  all  animals,  including 
the  vertebrates,  can  be  derived. 


92  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

3.  Study  of  the  microscopic  structure. — The  slides  contain  sections  in  front 
of,  through,  and  behind,  the  pharynx.     All  three  sections  should  be  made  use 
of  in  the  following  examination. 

The  structure  of  Planaria  differs  from  that  of  Hydra  in  that  a  third  layer, 
the  mesoderm,  composed  of  muscles  and  connective  tissue  is  present  between 
the  ectoderm  and  entoderm.  Planaria  is  therefore  a  triploUastic  animal,  con- 
sisting of  three  germ  layers.  In  the  sections  the  ventral  side  is  the  flattened  side ; 
the  dorsal  side  the  convex  side. 

a)  Ectoderm:  This  forms  a  thin  layer  of  ciliated  epithelial  cells,  the  epidermis. 
In  the  epidermis  may  be  distinguished  rodlike  bodies,  the  rhabdites,  which  when 
discharged  swell  and  form  mucus  and  mucus  cells,  containing  granules  which  are 
also  discharged  to  form  mucus.     These  mucus  cells  are  unicellular  glands. 

b)  Mesoderm:    Just  under  the  epidermis  is  a  thin  layer  of  circular  muscle 
cells.     Within  these  is  a  rather  indefinite  layer  of  longitudinal  muscle  cells 
which  appear  as  circles.     There  are  also  dorsoventral  muscles,  extending  between 
the  dorsal  and  ventral  sides,  between  the  branches  of  the  digestive  tract.    The 
rest  of  the  mesoderm  forms  a  characteristic  connective  tissue,  called  parenchyma, 
which  consists  of  branching  cells  and  fills  up  all  space  between  the  ectoderm  and 
entoderm  so  that  a  coelome  is  not  present. 

c)  Entoderm:    Each  section  contains  several  circular  hollow  masses  which 
are  the  cross-sections  of  the  digestive  tract.     The  wall  of  the  digestive  tract 
consists  of  a  single  layer  of  elongated  epithelial  cells,  which  are  the  entoderm 
cells.     These  are  generally  so  vacuolated  and  full  of  food  material  as  to  be  almost 
unrecognizable. 

•  d)  The  pharynx:  The  pharynx  lies  in  a  central  cavity,  the  pharyngeal  cham- 
ber. On  some  slides  the  ventral  opening  of  this  chamber,  the  mouth  opening, 
may  be  present.  The  pharynx  is  an  outgrowth  of  the  body  wall  which  has  come 
to  lie  in  a  depression  of  the  body  wall,  the  pharyngeal  chamber.  The  pharyngeal 
chamber  is  therefore  lined  with  ectoderm,  and  the  pharynx  is  covered  and  lined 
with  ectoderm,  the  same  as  the  outer  layer  of  the  body.  The  remainder  of  the 
pharynx  is  mesodermal,  consisting  of  circular,  longitudinal,  and  radiating  muscle 
fibers,  which  the  student  should  by  this  time  be  able  to  recognize,  and  parenchyma 
between  these. 

e)  The  ventral  nerve  cords:  These  can  usually  be  recognized  (best  on  sections 
anterior  to  the  pharynx)  as  pale,  round  areas,  near  the  ventral  surface,  about 
one-third  to  nearly  one-half  of  the  distance  out  from  the  median  line.  The 
pale  portion  consists  of  nerve  fibers;  often  a  few  nerve  cells,  large  cells  with 
large  nuclei,  will  be  found  along  the  dorsal  border  of  the  mass  of  fibers.  Make 
a  diagram  of  the  cross-section  through  the  pharynx. 

4.  Feeding  experiment. — Demonstration.     Observe  the  behavior  of  Planaria 
when  meat  is  put  into  the  pan.     Do  they  recognize  the  presence  of  food? 
How?     After  the  animals  have  attached  themselves  to  the  meat  gently  lift  one 


PHYLUM  PLATYHELMINTHES 


93 


up  and  observe  quickly  the  white  protruded  pharynx  which  is  inserted  into 
the  meat. 

5.  Regeneration.— To  save  time  and  material  members  of  each  table  may 
work  together  on  the  following  experiment:   Obtain  several  finger  bowls  and 
glass  covers  for  them  and  wash  both  thoroughly.    Take  several  Planaria  and 
cut  them  up  into  pieces  of  various  shapes  and  sizes.     Cut  some  very  small 
pieces.     The  animals  are  best  cut  by  placing  them  on  a  glass  plate,  waiting  until 
they  extend  to  their  full  length,  and  then  making  cuts  with  a  quick,  firm  stroke 
of  a  sharp  scalpel.     Place  the  pieces  in  the  finger  bowls  with  plenty  of  water, 
cover  with  glass  plates,  keep  out  of  the  sun,  and  change  the  water  every  few  days. 
Examine  at  each  laboratory  period  to  observe  the  progress  of  the  regeneration. 
Make  a  series  of  simple  outline  drawings  to  show  the  changes  in  form  from  day 
to  day. 

Is  any  piece  of  Planaria  capable  of  regenerating  a  whole  worm?  Are  any 
differences  apparent  due  to  differences  in  size  or  shape  of  the  original  pieces? 
Do  very  small  pieces  regenerate  as  well  as  larger  ones? 

6.  General  considerations  on  Planaria. — What  systems  does  Planaria  possess 
in  common  with   Hydra?    Are  these  better  developed  in  Planaria  than  in 
Hydra?    What  system  is  present  in  Planaria  which  was  entirely  lacking  in 
Hydra  ?    What  systems  are  absent  in  Planaria  which  the  frog  possesses?    What 
type  of  tissue  is  present  in  Planaria  which  Hydra  lacked?    How  do  the  muscle 
systems  of  the  two  animals  differ?    Is  the  digestive  tract  of  Planaria  a  gastro- 
vascular  system  as  in    Hydra,  i.e.,  both  digestive  and  distributive?    Does 
Planaria  still  retain  the  protozoan  method  of  digestion,  as  in  Hydra  (Hegner, 
p.  155)?    What  is  the  essential  difference  between  cross-sections  of  Hydra  and 
Planaria?    Understand  fully  what  are  the  corresponding  layers  in  the  two  ani- 
mals.   To  what  stage  in  the  development  of  the  frog  may  the  Planaria  be  com- 
pared? 

B.   GENERAL  SURVEY  OF  OTHER  FLATWORMS 

Examine  the  specimens  provided  and  familiarize  yourself  with  the  following 
groups  of  flatworms: 

1.  Free-living  flatworms  or  Turbellaria. — These  are  slender,  flat  animals 
similar  in  appearance  to  Planaria,  living  in  water  or  damp  places,  never  of  large 
size,  often  quite  small.     If  living  forms  other  than  Planaria  are  available  they 
will  be  demonstrated  to  you. 

2.  Flukes  or  trematodes.— These  flatworms  are  external  or  internal  parasites 
on  other  animals,  particularly  on  vertebrates.     They  are  broad,  flattened,  often 
leaflike  animals,  provided  with  suckers  and  hooks  for  adhesion  to  their  hosts. 
The  liver  fluke,  one  of  the  largest  forms,  lives  in  the  bile  ducts  of  sheep  and 
other  domestic  animals.     The  assistant  should  demonstrate  living  flukes  para- 
sitic in  the  frog.     The  commonest  are  the  lung  fluke,  Pneumoneces,  found  inside 


94  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

of  the  lungs  of  the  frog;  the  bladder  fluke,  Gorgoderina,  inside  the  urinary  bladder; 
and  Clinostomum,  occurring  in  cysts  in  the  peritoneum.  Eggs  and  embryos  of 
flukes  frequently  occur  in  the  frog  also. 

3.  Tapeworms  or  cestodes. — The  tapeworms  are  degenerate  flatworms  living 
as  internal  parasites,  commonly  in  the  digestive  tracts  of  vertebrates.  They 
are  extremely  long,  tapelike  animals,  as  the  name  implies,  with  a  small  head, 
provided  with  hooks  or  suckers  or  both  for  clinging,  and  a  body  made  up  of  a 
great  number  of  joints,  or  proglottids.  Each  proglottid  contains  a  complete 
set  of  the  complicated  reproductive  organs,  and  when  ripe  they  drop  off  from 
the  posterior  end  of  the  worm  so  as  to  infect  new  animals. 


XH.     PHYLUM  ANNELIDA 

A.      PRELIMINARY   STUDY  OF  NEREIS 

Nereis  is  an  annelid  living  in  the  mud  along  the  shores  of  the  ocean.  It  is 
a  relatively  simple  annelid  and  therefore  used  here  to  illustrate  certain  points. 
The  dissection,  however,  will  be  done  upon  the  earthworm,  a  more  specialized 
form,  but  one  more  easily  dissected. 

i.  External  anatomy  of  Nereis. — Place  a  specimen  in  a  dissecting  pan. 
Compare  general  form  and  symmetry  with  animals  previously  studied.  Is  it 
bilaterally  symmetrical?  The  most  striking  feature  of  the  body  is  its  division 
into  a  longitudinal  series  of  rings,  called  segments,  metameres,  or  somites.  In  this 
respect  Nereis  shows  a  marked  advance  over  Planaria  and  resembles  the  frog. 
Each  segment  bears  a  pair  of  broad  lateral  outgrowths,  the  parapodia,  by  means 
of  which  the  animal  swims.  Distinguish  anterior  and  posterior  ends,  dorsal 
(rounded)  and  ventral  (flattened)  surfaces. 

a)  Head:  The  first  segment  of  the  body  is  markedly  differentiated  as  a 
head,  which  bears  a  number  of  sense  organs.  The  head  segment  consists  of  two 
parts,  a  dorsal  squarish  projection,  the  prostomium,  which  does  not  extend  to 
the  ventral  side,  and  just  behind  this  a  complete,  ringlike  segment,  the  peri- 
stomium,  which  surrounds  the  mouth.  (In  most  specimens  the  large  pharynj 
will  be  found  protruded  from  the  mouth  so  as  to  extend  some  distance  anterior 
to  the  head.  This  should  not  be  confused  with  the  true  head.) 

The  sense  organs  of  the  head  consist  of  tentacles,  palps,  and  eyes.  There  are 
two  short  terminal  tentacles  projecting  from  the  middle  of  the  anterior  edge  of 
the  prostomium.  Lateral  to  these  on  each  side  is  a  thick  jointed  palp.  On  the 
dorsal  surface  of  the  prostomium  are  four  eyes,  indistinct  blackish  spots  situated 
so  as  to  form  the  four  corners  of  a  trapezoidal  area.  The  two  posterior  eyes  are 
likely  to  be  concealed  under  the  anterior  edge  of  the  peristomium.  The  eyes  of 
Nereis  are  much  more  complex  than  those  of  Planaria  and  are  provided  with 
lenses,  so  that  the  animal  can  probably  distinguish  objects  in  a  dim  way.  The 
peristomium  bears  four  conspicuous,  long,  lateral  tentacles,  or  cirri,  on  each  side. 
It  is  probable  that  tentacles  and  palps  are  organs  of  touch,  contact,  chemical 
sense,  etc.  It  is  known  that  they  are  thickly  strewn  with  sensory  nerve  cells. 

The  head  of  Nereis  therefore  represents  another  step  in  advance  in  the  series 
of  animal  forms  which  we  are  considering  in  that  it  is  more  sharply  differentiated 
from  the  rest  of  the  body  than  is  the  case  in  the  coelenterates  and  flatworms, 
and  it  is  provided  with  a  greater  variety  of  sense  organs  and  more  complex  and 
sensitive  ones. 

9S 


96  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

b)  Posterior  end'   The  last  segment  differs  from  the  others  in  that  it  bears 
no  parapodia.     A  central  opening,  the  anus,  is  present,  and  two  long  tentacles, 
or  cirri,  project  from  the  segment.     The  presence  of  the  anus  marks  another 
advance  over  the  previous  forms  in  which  the  digestive  tract  has  only  one 
opening.     In  this  respect  again  Nereis  resembles  the  frog. 

c)  Remainder  of  the  body:  Note  that  with  the  exception  of  the  first  and  last 
segments  all  the  segments  of  the  body  are  alike,  not  considering  minor  differences 
in  the  size  and  shape  of  the  parapodia.     This  similarity  of  segments  is  not  merely 
superficial  but  includes  the  entire  internal  anatomy.    The  same  parts  will  be 
found  repeated  in  each  segment.     Nereis  is  thus  an  ideal  segmented  animal. 

d)  Parapodium:    Cut  off  one  of  these  with  a  scissors,  mount  in  water,  cover, 
and  examine  with  the  low  power  of  the  microscope.     The  parapodium  consists 
of  several  lobes,  one  of  which,  the  gill  plate,  is  very  large  and  leaflike,  and  serves 
as  a  respiratory  organ.     In  some  relatives  of  Nereis  it  is  transformed  into  a 
filamentous  branched  gill.     Observe  the  stiff  bristles,  setae  or  chaetae,  which 
project  from  the  parapodium.     They  are  characteristic  annelid  structures. 

B.   THE  ANATOMY  OF  THE  EARTHWORM 

i.  External  anatomy  (Hegner,  chap,  x,  pp.  164-68). — Obtain  a  preserved 
specimen,  place  in  the  dissecting  pan,  and  compare  with  Nereis  as  to  form,  sym- 
metry, segmentation,  etc.  Are  the  two  animals  similar?  Distinguish  anterior 
and  posterior  ends,  dorsal  (dark-colored,  rounded)  and  ventral  (light-colored, 
flattened)  surfaces.  Is  the  head  as  well  developed  as  in  the  case  of  Nereis? 
Is  this  related  to  the  habit  of  life  of  the  earthworm?  The  head  of  Nereis  is  to  be 
regarded  as  a  typical  annelid  head,  while  that  of  the  earthworm  is  degenerate. 
Are  parapodia  present? 

a)  Head:  The  first  segment  is  composed,  as  in  Nereis,  of  a  prostomium,  the 
liplike  process  dorsal  to  the  mouth  opening,  and  the  peristomium,  the  ring 
surrounding  the  mouth.     The  head  of  the  earthworm  probably  consists  of  the 
first  four  or  five  segments,  as  indicated  by  experiments  in  regeneration.     No 
eyes  or  other  sense  organs  are  present  on  the  head  (this  being  also  associated 
with  the  habits  of  the  earthworm)  but  numerous  sensory  cells  are  imbedded  in 
the  epidermis  of  the  head  and  elsewhere. 

b)  Clitellum:    Anterior  to  the  middle  of  the  worm  a  number  of  swollen 
segments  occur,  producing  a  distinct  girdle  around  the  body,  called  the  clitellum. 
The  clitellum  is  a  glandular  region  which  secretes  the  cocoon  in  which  the  eggs 
of  the  earthworm  are  laid.     On  the  ventral  surface  of  the  clitellum  is  a  pair  of 
thickened  ridges,  the  tubercula  pubertatis.    How  many  segments  are  there  in  the 
clitellum?     How  many  segments  anterior  to  the  first  clitellar  segment?     Is 
this  number  the  same  in  all  individuals?    Remember  that  the  prostomium  is 
not  a  segment. 


PHYLUM  ANNELIDA 


97 


c)  External  openings:   The  mouth  opening  in  the  peristomium  has  already 
been  noted.     The  last  segment  contains  the  anus.     On  the  ventral  surface  of 
the  fifteenth  segment  is  a  pair  of  conspicuous  openings  with  swollen  lips,  the  ends 
of  the  male  ducts.     The  openings  of  the  female  ducts  are  on  the  fourteenth 
segment  and  much  smaller  than  the  male  openings  but  not  especially  difficult 
to  find  on  large  specimens.     There  are  also  the  openings  of  the  two  pairs  of 
seminal  receptacles  on  the  ninth  and  tenth  segments,  a  pair  of  excretory  openings 
on  the  ventral  surface  of  each  segment,  except  the  first  three  and  the  last,  and 
dorsal  openings,  the  dorsal  pores,  connected  with  the  coelome,  but  all  of  these 
are  minute  and  impossible  to  find. 

d)  Setae:    The  earthworm,  like  Nereis,  bears  setae  which  are  arranged  in 
four  double  longitudinal  rows,  two  ventral  and  two  lateral.     Pass  your  finger 
up  and  down  the  earthworm  and  feel  the  setae  as  rough  projections.     With  a 
hand  lens  make  out  their  arrangement  on  each  segment;   the  anterior  part  of 
the  body  is  the  most  favorable  place  to  see  them.     They  are  used  by  the  earth- 
worm to  prevent  slipping.     Make  a  diagram,  representing  a  segment  as  a  ring 
and  show  the  position  of  the  setae  on  the  ring. 

2.  Internal  anatomy  (Hegner,  pp.  168-69). — 

a)  Structure  of  the  body  wall,  coelome,  mesenteries:  The  body  is  covered  with 
an  iridescent  thin  cuticle  which  is  secreted  by  the  epidermis.  Strip  off  a  small 
piece,  spread  out  on  a  slide  in  a  drop  of  water,  cover,  and  examine  with  the  high 
power.  It  shows  striations  at  right  angles  to  each  other,  which  are  the  cause  of 
the  iridescence,  and  numerous  pores,  which  are  the  openings  of  the  gland  cells 
of  the  epidermis  to  the  exterior.  Draw  a  small  portion  of  the  cuticle. 

With  a  scissors  cut  through  the  body  wall  a  little  to  the  left  of  the  median 
dorsal  line  from  a  point  beginning  about  an  inch  behind  the  clitellum  and  extend 
the  cut  up  to  the  prostomium.  Be  careful  not  to  cut  through  anything  but  the 
body  wall;  if  black  material  oozes  out  you  may  know  that  you  are  cutting  into 
the  intestine  and  should  withdraw  your  scissors  and  begin  again  less  deeply.  Sepa- 
rate the  edges  of  the  cut  and  look  inside.  Observe  that  the  body  wall  is  separated 
from  the  intestine,  the  central  dark  tube,  by  a  distinct  space,  the  coelome.  Ob- 
serve further  that  this  space  is  not  continuous  but  is  divided  up  into  a  series  of 
compartments  by  delicate  white  partitions,  the  septa  or  mesenteries,  which 
extend  from  the  body  wall  to  the  intestine.  What  is  the  relation  of  these  septa 
to  the  external  rings?  The  coelome  of  the  earthworm  thus  consists  of  a  longi- 
tudinal series  of  chambers,  which  are  paired,  that  is,  one  on  each  side,  the  intestine 
being  inclosed  between  the  two  members  of  each  pair.  The  inner  walls  of  each 
pair  of  coelomic  compartments  therefore  meet  above  and  below  the  intestine 
to  form  dorsal  and  ventral  mesenteries,  although  these  are  no  longer  complete 
in  the  adult  worm.  The  anterior  and  posterior  walls  of  each  compartment 
come  in  contact  with  the  walls  of  those  in  front  of  and  behind  it,  producing 
double- walled  partitions,  the  septa  already  mentioned.  The  outer  wall  of  the 


98  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

compartment  is  fused  with  the  inside  of  the  body  wall,  forming  a  parietal  peri- 
toneum, while  the  inner  wall  is  similarly  attached  to  the  intestine,  forming  a 
visceral  peritoneum.  The  relations  therefore  of  the  coelome  and  its  linings  are 
identical  with  those  that  we  found  in  the  frog,  except  that  the  segmental  septa 
are  absent  in  the  latter. 

Cut  through  the  septa  so  that  you  can  lay  out  the  body  wall.  In  this  opera- 
tion it  is  best  to  stick  a  pin  through  the  body  wall  on  the  left  side;  then  lift  up 
the  other  side  of  the  cut  and  cut  through  the  septa  and •  pin  out  the  right  side; 
then  move  forward  a  short  distance  and  repeat.  Do  not  pull  the  wall  apart 
but  cut  the  septa  with  a  fine  scissors.  Stick  the  pins  in  obliquely  and  firmly 
so  that  they  will  not  get  in  your  way  and  will  not  come  out.  Open  up  the  body 
to  the  prostomium.  Note  the  iridescent  membrane,  the  peritoneum,  which  lines 
the  body  wall.  Cover  the  animal  completely  with  water. 

Before  beginning  a  detailed  dissection  of  the  various  systems,  the  following 
conspicuous  structures  should  be  identified.  The  center  of  the  body  is  occupied 
by  the  long  brownish  intestine.  In  the  tenth,  eleventh,  and  twelfth  segments 
are  pairs  of  large  white  bodies.  These  are  the  seminal  vesicles,  part  of  the  male 
reproductive  system.  In  the  ninth  and  tenth  segments  are  pairs  of  small  white 
spherical  bodies,  the  seminal  receptacles,  part  of  the  female  reproductive  system. 
Loose  white  objects  on  each  side  of  the  intestine  along  its  entire  length  are  the 
excretory  organs,  or  nephridia. 

b)  The  circulatory  system:  This  system  is  difficult  and  unsatisfactory  to 
make  out  in  dissection  owing  to  the  small  size  of  the  vessels,  and  the  student  is 
referred  to  Hegner  (pp.  172-75)  for  details.  The  following  parts  should  be  noted: 

(1)  The  dorsal  blood  vessel:  This  is  the  dark  brownish  line  running  along  the 
median  dorsal  surface  of  the  intestine.     In  many  specimens  the  two  pairs  of 
branches  which  it  receives  in  each  segment  from  the  wall  of  the  intestine  can  be 
seen.    Its  branches  from  the  body  wall  (torn  off,  of  course)  may  also  be  found 
sometimes.    Look  for  these. 

(2)  The  hearts:  Remove  the  seminal  vesicles  from  the  left  side.    Note  that 
in  the  region  where  they  were  located  and  for  some  distance  anterior  to  this  the 
septa  are  stronger  and  more  conspicuous  than  elsewhere,  projecting  out  from 
the  intestine  like  wings.    Look  in  the  eleventh  segment,  between  the  places 
occupied  by  the  second  and  third  seminal  vesicles,  for  a  pair  of  stout  tubes 
arising  from  the  dorsal  vessel  and  extending  ventrally.     They  are  often  dark- 
colored  because  of  contained  blood.     Then  look  in  each  segment  forward  from 
this  up  to  the  sixth  for  a  similar  pair  of  tubes,  grasping  the  winglike  septa  with 
a  forceps  and  pulling  them  backward.     These  branches  of  the  dorsal  vessel, 
found  in  the  seventh  to  the  eleventh  segments,  are  contractile  tubes,  inappro- 
priately called  hearts.    The  first  pair  is  quite  small.     More  than  five  pairs  are 
sometimes  found.     Follow  the  dorsal  vessel  forward  as  far  as  you  can  beyond  the 
region  of  the  hearts. 


PHYLUM  ANNELIDA  99 

(3)  The  ventral  blood  vessel:  Loosen  up  the  intestine  completely  on  the  left 
side  so  that  it  can  be  pressed  over  to  the  right  side  to  enable  you  to  see  the 
median  ventral  line.     Look  here  on  the  underside  of  the  intestine  for  a  brownish 
line,  the  ventral  blood  vessel.     It  is  easiest  to  see  under  the  dilated  portion  of 
the  intestine  behind  the  region  of  the  seminal  vesicles.    Look  for  branches  of 
the  ventral  blood  vessel  to  the  intestine,  body  wall,  and  the  nephridia.     Trace 
the  connection  of  the  hearts  with  the  ventral  blood  vessel  and  follow  the  latter 
forward  as  far  as  you  can. 

(4)  The  subneural  vessel:  Directly  under  the  ventral  blood  vessel  is  a  white 
line,  the  ventral  nerve  cord.     Cut  this  through  at  some  convenient  point  back  of 
the  region  of  the  hearts,  pull  up  a  short  strip  of  it  backward,  and  look  on  the 
underside  for  a  longitudinal  vessel  looking  like  a  dark  line  running  down  the 
middle  of  the  white  cord.     Its  branches  from  the  nephridia  and  the  body  wall 
may  sometimes  be  found.     It  is  called  the  subneural  vessel. 

(5)  The  intestino-tegumentary  vessels:    Extending  from  the  tenth  segment 
forward,  an  extra  vessel  will  be  found  on  each  side  of  the  wall  of  the  intestine. 
Hearts  and  other  structures  should  be  removed  to  see  it. 

Make  a  drawing  from  the  side  of  the  parts  of  the  circulatory  system  which 
you  have  been  able  to  find.  Some  specimens  will  show  more  of  the  vessels  than 
others. 

On  living  earthworms  observe  the  rhythmic  contractions  of  the  dorsal  vessel. 
In  which  direction  do  the  contractions  travel?  Read  Hegner  (p.  175)  on  the 
course  of  the  circulation  in  the  earthworm. 

c)  The  digestive  system:  It  consists  of  the  following  parts  (Hegner, 
pp.  169-71): 

(1)  Buccal  pouch:  This  is  a  small  tube  extending  from  the  mouth  through 
about  three  segments.     White,  slender,  muscle  fibers,  the  dilators  of  pharynx, 
attach  it  to  the  body  wall  and  allow  of  its  expansion.     On  the  dorsal  surface 
of  the  buccal  pouch,  just  before  the  pharynx  begins,  note  the  small,  white, 
bilobed  brain. 

(2)  Pharynx:   This  is  the  thick-walled  portion  following  the  buccal  pouch. 
The  muscular  fibers  attaching  it  to  the  body  wall  are  much  more  numerous  than 
in  the  preceding  division. 

(3)  Esophagus:  This  long,  slender  tube  extends  through  the  region  occupied 
by  the  hearts  and  seminal  vesicles.     These  should  be  removed  from  the  left  side, 
if  not  already  done,  so  that  it  can  be  clearly  seen.     In  its  wall  in  the  region  of  the 
seminal  vesicles  are  three  pairs  of  brownish  projections,  the  calciferous  glands, 
said  to  secrete  calcium  carbonate  into  the  digestive  tract. 

(4)  Crop:   The  esophagus  leads  into  the  large  thin-walled  crop,  which  acts 
as  a  storage  reservoir  for  food. 

(5)  Gizzard:    Immediately  posterior  to  the  crop  is  the  very  thick-walled 
gizzard,  in  which  the  food  is  ground  to  small  particles. 


ioo  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOQ.Y 

(6)  Intestine:  From  the  gizzard  the  brown  thin-walled  intestine  extends 
straight  posteriorly  to  the  anus.  Its  brown  color  is  due  to  peculiar  cells,  the 
chlorogogue  cells,  which  cover  it.  Cut  open  the  intestine  for  a  short  distance 
along  one  side,  wash  it  out  and  observe  a  thickening  in  its  median  dorsal  wall. 
This  thickening,  the  typhlosole,  is  a  longitudinal  infolding  of  the  dorsal  wall, 
apparently  for  the  purpose  of  increasing  the  absorbing  surface  of  the  intestine, 
for  which  function  it  is  still  further  folded  by  transverse  grooves. 

Draw,  showing  all  parts  of  the  digestive  system  in  relation  to  the  segments, 
properly  numbered.  This  drawing  may  be  combined  with  that  of  the  circu- 
latory system,  if  desired. 

d)  The  excretory  system  (Hegner,  pp.   175-76):    The  excretory  system  of 
the  earthworm  consists  of  a  pair  of  coiled  tubes  in  each  segment  (except  the 
first  three  and  the  last).     Each  tube  is  called  a  nephridium.     The  main  part 
of  each  nephridium  consists  of  a  tube  coiled  transversely  in  the  coelome  of  the 
segment  and  opening  to  the  exterior  of  that  segment  by  a  nephridiopore.     The 
beginning  of  the  coiled  tube  is  situated,  however,  in  the  segment  anterior  to  the 
one  where  the  main  structure  is  located;   the  tube  penetrates  the  septum  and 
opens  into  the  coelome  of  the  preceding  segment  by  a  funnel,  called  the  nephro- 
stome.     The  nephridia  are  readily  recognizable  as  the  white  loose  structures 
on  the  sides  of  the  digestive  tract.     Extend  your  original  incision  about  one  inch 
backward,  this  time  exactly  in  the  median  dorsal  line.     Open  out  the  wall  as 
before  by  cutting  the  septa.     Pull  out  the  intestine.     Pin  out  the  body  wall 
tightly.     Observe  with  the  hand  lens  the  paired  nephridia  in  each  segment.     By 
manipulating  the  septa  you  should  have  no  difficulty  in  seeing  the  tube  pene- 
trating the  septum  and  ending  in  the  segment  in  front  by  the  funnel,  appearing 
as  a  white  spot.     Cut  out  a  nephridium  as  completely  as  possible,  mount  on  a 
slide  in  water,  and  cover.     Examine  with  the  low  power.     Identify  the  nephro- 
stome  (see  Hegner,  Fig.  89,  p.  176);   the  thin  tube  which  passes  through  the 
septum,  and  forms  the  first  slender  loop  of  the  coiled  portion;  and  the  remaining 
wider  loops. 

e)  The  reproductive  system:    The  dissection  of  the  reproductive  system  is 
rather  difficult  and  should  be  attempted  only  on  large  and  well-preserved  speci- 
mens.    By  constant  reference  to  Hegner  (Fig.  93,  p.  181)  and  by  exercising  the 
utmost  care  in  dissection  the  student  will  probably  be  able  to  find  the  parts  of 
the  reproductive  system.     As  in  Planaria,  a  complete  set  of  both  male  and  female 
organs  occurs  in  the  earthworm,  that  is,  it  is  hermaphroditic. 

The  right  side  of  your  specimen  has  been  preserved  intact  for  this  dissection. 
Remove  the  esophagus  carefully  from  the  region  of  the  seminal  vesicles  (no  farther) 
and  study  their  arrangement.  The  first  pair  are  rounded  sacs  projecting  forward 
into  the  ninth  segment  above  the  first  pair  of  seminal  receptacles.  The  second 
vesicles  are  more  elongated  and  folded  and  occupy  the  eleventh  segment.  The 
third  vesicles  are  the  largest  and  are  much  folded,  occupying  the  twelfth  and 


PHYLUM  ANNELIDA  101 

part  of  the  thirteenth  segments.  The  three  pairs  are  united  by  median  masses 
located  in  the  tenth  and  eleventh  segments.  Locate  the  fifteenth  segment  and 
stick  a  pin  into  it  as  a  landmark.  Gently  press  the  vesicles  and  intestine  to  the 
left  and  pull  off  the  nephridia  from  the  right  ventral  body  wall  by  grasping  their 
free  ends.  Stretch  out  the  right  ventral  wall  tightly.  Locate  on  it  the  ventral 
edge  of  the  dorsal  longitudinal  muscle  band,  extending  as  a  longitudinal  line. 
Within  and  in  contact  with  this  will  be  found  the  lateral  setae,  projecting  inward 
as  minute  white  elevations,  with  a  slender  muscle  band  between  the  two  members 
of  the  pair.  One-third  of  the  way  between  the  row  of  setae  and  the  ventral 
nerve  cord  find  a  white  line  extending  from  the  middle  of  the  fifteenth  segment 
forward  to  the  tenth.  This  is  the  vas  deferens  or  male  duct.  Examine  the  septum 
between  the  fourteenth  and  thirteenth  segments.  The  white  object  in  it  is  the 
oviduct  with  a  slender  tube  extending  into  the  fourteenth  segment.  Then  examine 
the  septum  between  the  twelfth  and  thirteenth  segments.  A  minute  white  body, 
the  ovary,  will  be  found  attached  to  it.  The  attached  end  is  the  broadest;  the 
free  slender  pointed  end  projects  backward  into  the  thirteenth  segment.  If 
you  are  in  any  doubt  that  you  have  the  ovary,  remove  it  and  examine  it  with 
the  microscope,  and  the  presence  of  round  eggs,  the  largest  of  which  are  in  the 
pointed  extremity,  will  settle  the  matter.  Next  look  in  the  twelfth  segment 
for  a  slender  branch  extending  from  the  vas  deferens  over  to  the  fused  median 
portion  of  the  seminal  vesicles.  Dissect  off  the  roof  of  the  median  portion  of 
the  seminal  vesicle  in  the  eleventh  segment  and  note  within  its  cavity  the  greatly 
folded  seminal  funnel.  Anterior  to  this,  attached  to  the  septum  between  the 
tenth  and  eleventh  segments,  will  be  found  by  cautiously  picking  away  the 
bases  of  the  seminal  vesicles  a  small  but  distinct  round  body,  the  testis.  Repeat 
the  directions  in  the  three  preceding  sentences  in  the  eleventh  and  tenth  segments, 
and  find  the  anterior  branch  of  the  vas  deferens,  the  anterior  seminal  funnel,  and 
the  anterior  pair  of  testes.  The  mother-cells  of  the  sperm  are  produced  in  the 
testes  and  set  free  at  an  early  stage  into  the  seminal  vesicles,  in  which  they  develop 
into  sperm.  Take  out  a  small  piece  of  the  seminal  funnel,  put  on  a  slide  in  a 
drop  of  water,  cover,  and  mash  by  pressing  on  the  cover  glass  with  the  finger 
and  rotating  it.  Examine  with  the  high  power  and  note  the  myriads  of  slender- 
tailed  spermatozoa.  The  two  rounded  seminal  receptacles  in  the  ninth  and  tenth 
segments  were  previously  noted.  They  receive  the  sperm  from  another  animal 
during  copulation  and  are  therefore  parts  of  the  female  system. 
Draw  the  reproductive  system. 

/)  The  nervous  system:   Remove  the  digestive  system  as  far  forward  as  the 
pharynx  (Hegner,  pp.  176-80).     The  ventral  nerve  cord,  a  white  cord  in  the 
median  ventral  line,  has  already  been  identified.     Clean  away  all  tissue  conceal- 
ing it.     Examine  it  with  a  hand  lens  and  note  the  enlargements  or  ganglia  which 
re  present  in  the  cord  in  the  middle  of  each  segment  and  the  lateral  branches 
rhich  arise  from  it.     Cord  and  ganglia  are  really  double,  formed  by  the  median 


102  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

fusion  of  two  originally  separate  cords  (as  in  Planaria) ,  but  the  double  character 
appears  externally  only  in  the  anterior  part  of  the  system.  Trace  the  nerve 
cord  anteriorly.  Loosen  the  pharynx  and  turn  it  forward.  Find  underneath 
it  the  anterior  termination  of  the  ventral  cord  in  a  large  double  mass,  the  sub- 
esophageal  ganglia.  Locate  the  brain  on  the  dorsal  side  of  the  buccal  pouch  and 
cut  away  the  pharynx  and  as  much  of  the  buccal  pouch  as  you  safely  can,  leaving 
the  brain  in  place.  Note  the  two  cords  which  extend  dorsally  from  the  sub- 
esophageal  ganglia  to  the  brain,  forming  a  circle  through  which  the  buccal  pouch 
passes.  These  cords  are  called  the  circumesophageal  connectives.  Examine  the 
brain  and  note  that  it  consists  of  two  distinct  lobes,  the  supra-esophageal  ganglia. 
Find  the  nerves  running  forward  from  the  brain  to  the  prostomium  and  from  the 
connectives  to  the  ventral  portions  of  the  first  segments. 

Draw  the  nervous  system. 

Strip  off  a  piece  of  the  ventral  nerve  cord,  preferably  near  the  anterior  end, 
mount  it  in  water  on  a  slide  and  examine  with  the  low  power.  Find  out  how 
many  lateral  nerves  pass  out  from  each  ganglion  and  how  many  arise  between 
the  ganglia,  and  put  this  in  your  drawing.  You  will  probably  notice  the  sub- 
neural  blood  vessel  and  its  branches  on  the  ventral  surface  of  the  cord.  Do  not 
confuse  these  with  nerves;  they  are  generally  yellowish  and  hollow,  while  the 
nerves  are  white  and  longitudinally  striped. 

g)  Cross-section  of  the  earthworm:  Make  a  straight,  clean  cut  across  the  earth- 
worm in  the  center  of  a  segment,  that  is,  just  halfway  between  two  rings.  Use 
the  posterior  part  of  the  worm  which  has  not  been  opened.  Make  another  cross- 
cut near  the  first  one  so  as  to  separate  off  a  small  section  of  the  worm.  Wash 
out  the  contents  of  the  intestine  in  the  piece  and  place  it  under  water  with  the 
first  cut  surface  up.  Examine  with  a  hand  lens.  Identify  in  the  body  wall 
the  outer  white  epidermis,  and  under  this  the  thicker  greenish  layer  composed  of 
longitudinal  muscles.  Observe  in  this  the  four  pairs  of  setae  projecting  inward 
dividing  the  longitudinal  muscle  coat  into  bands.  Of  these  identify  the  dorsal 
bands,  extending  from  the  median  dorsal  line  to  the  lateral  setae,  the  lateral 
bands  between  the  lateral  and  ventral  bundles  of  setae,  and  the  ventral  band 
across  the  ventral  side.  Slender  bands  also  exist  between  the  two  members  of 
each  pair  of  setae.  In  the  intestine  identify  the  typhlosole.  Between  the  intes- 
tine and  the  body  wall  in  the  coelome  note  the  long  white  nephridia,  opening  to 
the  exterior  just  outside  the  ventral  setae.  In  the  median  ventral  line  above 
the  ventral  muscle  band  will  be  found  the  white  section  of  the  nerve  cord.  Gently 
lift  out  the  nephridia  and  observe  the  septum  stretching  across  the  coelome. 

Make  a  drawing  of  the  cross-section. 

3.  Microscopical  structure  of  the  earthworm. — Examine  slide  "Lumbricus" 
(Hegner,  Fig.  85,  p.  166). 

a)  General  appearance  of  the  cross-section:  Examine  with  the  low  power  and 
identify  the  thick  body  wall,  the  coelome  between  the  body  wall  and  the  intes- 


PHYLUM  ANNELIDA 


103 


tine,  and  the  intestine  with  its  dorsal  infolded  typhlosole  and  outer  covering  of 
peculiar  large  cells.  In  the  body  wall,  the  most  conspicuous  layer  is  the  feathery 
layer  of  longitudinal  muscles,  which  is  interrupted  in  eight  places,  four  lateral 
and  four  ventral  for  the  insertion  of  the  setae.  These  interruptions  divide  the 
longitudinal  muscle  coat  into  bands,  which  were  noted  in  the  preceding  paragraph 
in  the  cut  surface  of  the  earthworm  and  should  be  identified  again.  Identify 
the  dorsal  blood  vessel  lying  above  the  typhlosole  imbedded  in  the  large  pear- 
shaped  cells;  the  ventral  blood  vessel  below  the  intestine  to  which  it  is  attached 
by  a  ventral  mesentery;  and  the  ventral  nerve  cord  just  below  the  ventral  blood 
vessel.  In  the  coelome  may  be  seen  traces  of  nephridia,  blood  vessels,  and  septa. 
Make  a  diagram  of  the  section. 

b)  Structure  of  the  body  wall:   Examine  with  the  high  power,  and  study  the 
following  layers: 

(1)  Cuticle:  The  outermost  layer,  a  thin  non-cellular  covering. 

(2)  Epidermis:  This  contains  about  four  kinds  of  cells.     The  most  conspicu- 
ous are  the  gland  cells,  large  elliptical  cells  filled  with  granules,  which  are  fore- 
runners of  mucus.    These  gland  cells  open  to  the  surface  by  way  of  the  pores 
already  noted  in  the  cuticle.     Between  the  gland  cells  are  interstitial  cells, 
elongated  cells  with  broadened  ends.    At  the  bases  of  the  gland  and  interstitial 
cells  may  be  noted  some  small  cells,  which  are  sometimes  considered  to  be  a 
second  layer.     The  fourth  kind  of  cell,  sensory  cells,  cannot  be  seen  without 
special  methods  of  staining  (Hegner,  Fig.  86,  p.  167). 

(3)  Circular  muscle  layer:    This  consists  of  very  long  slender  muscle  cells 
imbedded  in  connective  tissue,  running  circularly. 

(4)  Longitudinal  muscle  layer :  This  consists  of  muscle  cells  like  those  of  the 
circular  layer,  but  as  they  run  longitudinally  they  appear  in  cross-sections  as 
circles  or  ellipses.    These  longitudinal  muscle  cells  are  mounted  on  plates  or 
septa  of  connective  tissue,  which  extend  out  from  the  body  wall  at  right  angles 
to  it.     This  arrangement  of  the  muscle  cells  along  these  septa  gives  a  feathery 
appearance  in  cross-section.     The  interruptions  of  the  longitudinal  muscles  for 
the  setae  have  already  been  noted. 

(5)  Peritoneum:  The  body  wall  is  lined  with  peritoneum,  a  very  thin  layer 
of  cells  applied  to  the  inner  surface  of  the  longitudinal  muscle  layer. 

(6)  Setae:   If  setae  are  present  on  your  slide  note  their  appearance.    They 
are  slender,  yellow,  curved  rods  of  the  same  composition  as  the  cuticle  and 
like  it  secreted  by  the  epidermis.     The  epidermis  turns  in  to  form  a  sheath 
around  each  seta  and  a  sort  of  cap  at  the  inner  end  of  the  seta,  where  the 
seta  is  secreted.    From  the  epidermal  sheath  and  cap  muscles  may  be  seen 
extending  to  the  circular  muscle  layer.    These  muscles  serve  to  move  the 
setae  in  all  directions. 

Draw  a  small  portion  of  the  body  wall  in  great  detail. 


104  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

c)  Structure  of  the  intestinal  wall:  Examine  with  the  high  power. 

(1)  Chlorogogue  cells:  The  outer  lay^er  of  the  intestine  consists  of  very  large, 
irregular,  somewhat  pear-shaped  cells  which  are  modified  peritoneal  cells.     They 
are  named  the  chlorogogue  cells.     . 

(2)  Longitudinal  muscle  layer:  At  the  inner  ends  of  the  chlorogogue  cells  a 
row  of  circles,  cross-sections  of  a  very  thin  layer  of  longitudinally  arranged  muscle 
cells,  appears. 

(3)  Circular  muscle  layer:  A  thin  layer  of  circularly  arranged  muscle  cells 
lies  just  within  the  preceding. 

(4)  Vascular  layer :  The  blood  vessels  of  the  intestine,  branches  of  the  dorsal 
and  ventral  blood  vessels,  run  in  a  definite  layer  in  the  wall  of  the  intestine  just 
within  the  circular  muscles.    Here  they  form  a  rich  network,  appearing  in  the 
section  as  irregular  spaces,  uniformly  stained. 

(3)  Lining  epithelium:  The  innermost  layer  of  the  intestinal  wall,  lining  the 
cavity,  is  an  epithelium,  consisting  of  long,  slender,  ciliated,  epithelial  cells. 
This  layer  is  almost  as  wide  as  the  layer  of  chlorogogue  cells.  The  nuclei  are 
near  the  bases  of  the  cells. 

Draw  a  portion  of  the  intestinal  wall  in  great  detail  to  show  these  layers. 

d)  Structure  of  the  nerve  cord:    Examine  with  the  high  power.     The  nerve 
cord  is  somewhat  oval  in  outline  and  is  covered  externally  by  a  sheath  consisting 
of  peritoneum,  connective  tissue,  muscles,  and  blood  vessels.     Of  these  the  more 
conspicuous  ones  are  the  subneural  vessel  on  the  median  ventral  side  and  the 
paired  lateral  neural  vessels,  one  on  each  side  of  the  subneural  vessel. 

The  cord  is  more  or  less  distinctly  divided  into  two  halves  by  a  median  parti- 
tion. On  the  dorsal  side  of  the  cord  are  three  large  clear  areas,  the  giant  fibers, 
believed  to  be  nerve  fibers  which  run  for  long  distances  in  the  worm.  Each  is 
surrounded  by  a  thick  sheath.  In  the  lateral  and  ventral  portions  of  the  cord 
may  usually  be  seen  several  large  pear-shaped  nerve  cells,  each  with  a  large 
nucleus  and  nucleolus.  The  nerve  cells  are  more  abundant  if  the  section  has 
happened  to  pass  through  one  of  the  ganglionic  swellings  of  the  cord.  The  rest 
of  the  cord  consists  of  cross-sections  of  nerve  fibers,  appearing  like  an  open 
network. 

Draw  the  section  of  the  nerve  cord. 

e)  Longitudinal  section  of  the  earthworm:  Study  and  identify  the  parts  already 
seen  in  the  cross-section.    Note  particularly  the  septa. 

4.  General  considerations  on  the  earthworm. — What  system  is  present  in 
the  earthworm  which  was  lacking  in  Planaria?  What  systems  which  the  frog 
possesses  are  lacking  in  the  earthworm?  How  do  you  think  the  earthworm 
compares  with  the  frog  with  respect  to  differentiation  of  organs  and  systems? 
What  particular  system  shows  the  least  advance  over  the  same  one  in  Planaria 
and  least  resembles  that  of  the  frog?  In  what  ways  does  the  digestive  tract  of 
the  earthworm  differ  from  that  of  Planaria  and  resemble  that  of  the  frog?  In 


PHYLUM  ANNELIDA 


105 


the  cross-section  of  the  earthworm  what  striking  differences  from  the  cross- 
section  of  Planaria  are  apparent?  Are  the  layers  of  the  body  wall  of  the  earth- 
worm the  same  in  general  as  those  of  the  body  wall  of  the  frog?  those  of  the 
intestine  of  the  two  animals?  In  comparing  the  cross-sections  of  Hydra, 
Planaria,  earthworm,  and  frog  one  may  note  the  following  points:  the  gastro- 
vascular  cavity  of  the  two  former  animals  corresponds  to  the  cavity  of  the  intes- 
tine of  the  two  latter;  the  lining  epithelium  of  the  intestine  in  earthworm  and 
frog  is  the  entoderm;  the  epidermis,  the  ectoderm;  and  all  of  the  tissue  in 
between  is  mesoderm. 

C.   GENERAL  SURVEY  OF  ANNELIDS 

1.  Polychaetes. — The  polychaetes  are  the  group  of  marine  annelids  to 
which  Nereis  belongs.     They  are  characterized  by  the  possession  of  parapodia. 
Examine  the  various  specimens  available.    Note  form  and  segmentation  of  the 
body,  development  of  parapodia,  presence  and  location  of  gills  (slender  respiratory 
processes,  often  arranged  in  clumps),  degree  of  development  of  the  head.     Many 
of  the  polychaetes  live  in  tubes  secreted  by  themselves,  and  hence  the  parapodia 
and  head  regions  are  often  degenerate. 

2.  Leeches. — Leeches  are  common  annelids  of  fresh  water,  readily  distin- 
guished by  the  presence  of  two  suckers,  one  at  each  end  of  the  body.     Examine 
the  specimens.     Are  parapodia  or  setae  present? 

3.  Oligochaetes. — This  group  includes  all  of  the  earthworms,  of  which  there 
are  many  different  kinds,  similar,  however,  in  structure,  and  also  a  number  of 
small  annelids,  which  live  in  fresh  water.  Some  of  these  latter,  known  as  naids, 
are  often  found  in  Protozoan  cultures  (see  p.  80,  le).  Other  of  the  fresh-water 
oligochaetes,  known  as  tubificids,  live  in  tubes  in  the  mud  in  the  bottom  of  ponds 
and  streams;  their  posterior  ends  project  into  the  water  and  carry  on  a  constant 
undulatory  motion  for  respiratory  purposes. 


XIII.     PHYLUM  ARTHROPOD  A 

A.      THE  ANATOMY  OF  THE   LOBSTER   (OR   CRAYFISH) 

For  this  study  either  the  lobster  or  the  crayfish  may  be  employed,  although 
the  former  is  preferable  because  of  its  greater  size.  The  slight  differences 
between  the  anatomy  of  these  two  animals  are  noted  in  the  course  of  the  out- 
line (Hegner,  chap,  xi,  pp.  193-225). 

i.  External  anatomy. — Obtain  a  preserved  specimen  and  place  in  a  dissecting 
pan.  The  animal  has  a  hard  external  covering,  the  exoskeleton,  which  cor- 
responds to  the  cuticle  of  the  earthworm,  and  it  is  a  secretion  of  the  ectoderm. 
It  is  composed  of  chitin,  rendered  hard  by  the  deposit  of  calcium  carbonate  in  it. 
Identify  anterior  and  posterior  ends,  dorsal  and  ventral  surfaces.  Is  the  animal 
bilaterally  symmetrical?  Is  it  segmented?  Is  it  clearly  segmented  along  the 
whole  axis  of  the  body,  like  the  annelids?  What  part  of  the  body  is  most  evi- 
dently segmented?  what  least? 

The  body  differs  greatly  from  the  other  invertebrates  studied  and  resembles 
the  frog  in  that  it  is  divided  into  definite  regions,  the  head,  thorax,  and  abdomen. 
Head  and  thorax  are,  however,  more  or  less  fused  into  one  region,  called  the 
cephalothorax.  The  single  piece  of  the  exoskeleton  which  covers  the  cephalo- 
thorax  dorsally  and  laterally  is  called  the  carapace.  A  groove  runs  across  the 
mid-dorsal  region  of  the  carapace  and  obliquely  forward  on  either  side.  This 
is  the  cervical  groove  and  separates  the  head  in  front  from  the  thorax  behind. 
Segmentation  has  been  lost  on  the  dorsal  side  of  the  cephalothorax  through 
fusion  of  segments. 

Another  striking  difference  between  the  lobster  and  the  other  invertebrates 
previously  studied  is  the  presence  of  jointed  appendages.  Each,  segment  of  the 
body  is  represented  by  a  pair  of  appendages,  and  it  is  thus  possible  to  determine 
the  number  of  segments  even  where  the  lines  between  them  have  been  lost  by 
fusion.  In  many  arthropods,  however,  some  of  the  appendages  have  been  lost 
also,  so  that  the  determination  of  the  number  of  segments  in  the  body  is  some- 
times a  matter  of  great  difficulty. 

a)  The  head:  The  head  terminates  anteriorly  in  a  spiny  pointed  projection 
of  the  carapace,  the  rostrum.  The  head  is  provided  with  a  number  of  sense 
organs,  exceeding,  in  vaiiety  and  complexity,  those  of  the  lower  invertebrates. 
There  is  a  pair  of  large,  stalked,  movable  eyes,  which  are  probably  not  appendages. 
In  front  of  the  eyes  occurs  the  first  pair  of  appendages,  the  antennules,  short, 
forked  filamentous  outgrowths.  Just  below  these  is  the  second  pair  of  append- 
ages, the  antennae,  long,  flexible,  many-jointed  structures.  Both  antennae  and 

106 


PHYLUM  ARTHROPODA 


107 


antennules  have  tactile  and  chemical  functions.  On  the  ventral  side  of  the 
head  are  additional  appendages  belonging  to  the  head,  surrounding  the  mouth 
and  used  for  tasting,  handling,  and  tearing  food.  These  will  be  studied  later. 

b)  The  thorax:   Two  longitudinal  lines  on  the  dorsal  surface  of  the  thorax 
divide  the  carapace  into  a  median  cardiac  region,  covering  the  heart,  and  two 
broad,  curved,  lateral  branchial  regions,  which  cover  the  chamber  containing  the 
gills.     The  ventral  side  of  the  thorax  bears  five  pairs  of  walking  legs,  of  which 
the  anterior  pair  is  modified  into  large  pincers;  some  of  the  appendages  in  front 
of  the  pincers  also  belong  to  the  thorax. 

c)  The  abdomen:   The  abdomen  is  plainly  divided  into  seven  joints  or  seg- 
ments, six  of  which  bear  appendages,  used  for  swimming.    The  first  pair  of 
abdominal  appendages  in  male  and  female  lobsters  and  in  female  crayfishes 
and  the  first  two  pairs  in  male  crayfishes  are  modified  for  sexual  purposes.    The 
last  pair  of  abdominal  appendages  is  greatly  broadened  and  forms  with  the  last 
abdominal  segment  a  broad  swimming  fan.    The  last  segment,  or  telson,  has 
no  appendages  and  bears  the  anus  on  its  median  ventral  surface.    There  is  some 
doubt  that  the  telson  is  a  true  segment. 

d)  Study  of  a  typical  segment  and  pair  of  appendages:    As  the  abdominal 
segments  are  more  distinct  and  less  modified  than  the  other  segments,  one  of 
them,  as  the  third  or  fourth,  may  be  selected  for  study.     Such  a  segment  has 
the  general  shape  of  a  ring,  as  in  the  annelids.     Its  exoskeletal  covering  may 
be  divided  into  a  convex  dorsal  portion,  the  tergum,  a  thin  lateral  plate,  the 
pleuron,  extending  free  ventrally  into  a  point,  and  a  slender  ventral  bar,  the 
sternum.    The  region  between  the  pleuron  and  the  base  of  the  appendage 
receives  the  name  of  epimeron.    Between  successive  segments  occur  thin  arthro- 
podial  membranes,  where  the  calcareous  deposit  is  lacking;   these  are  best  seen 
on  the  ventral  surface  between  successive  sterna,  and  they  permit  movement 
of  the  segments  upon  one  another.     Examine  the  joints  between  segments  at 
the  pleura;  determine  how  they  work  by  bending  and  straightening  the  abdomen. 

Between  the  base  of  the  pleuron  and  the  sternum  of  the  segment  is  a  round 
area,  into  which  the  appendage  is  fastened  by  means  of  an  arthropodial  mem- 
brane. Cut  through  this  membrane  and  remove  a  complete  appendage.  It  has 
the  following  parts:  It  springs  from  the  segment  by  a  basal  stem,  the  protopod. 
This  really  consists  of  two  joints,  a  very  small  basal  piece,  the  coxopod,  and  a 
long  distal  part,  the  basipod.  From  the  basipod  arise  two  flattened,  many- 
jointed  plates.  The  outer  of  these  is  the  exopod;  the  inner  one,  next  the  median 
line,  the  endopod.  Make  a  diagram  of  an  ideal  cross-section  of  the  segment 
with  its  pair  of  appendages. 

This  type  of  appendage  found  on  the  abdominal  segments  is  called  the  two- 
forked  or  biramous  appendage.  It  is  supposed  to  be  the  primitive  arthropod 
appendage,  all  other  kinds  of  appendages  found  in  arthropods  being  derived 
from  it  by  modification.  Theoretically,  the  original  arthropod  consisted  of  a 


io8  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

series  of  segments,  like  the  abdominal  segments  of  the  lobster,  all  bearing 
biramous  appendages. 

e)  Comparative  study  of  the  appendages:  The  appendages  will  be  studied  by 
comparing  them  with  the  typical  biramous  appendage  described  in  the  preceding 
section,  and  determining  what  modifications  have  occurred.  Consult  Hegner, 
Table  VII  (pp.  197-99). 

(1)  The  abdominal  appendages:  These  are  designated  as  swimmerets,  since 
they  are  employed  in  swimming.     In  the  female  they  also  serve  as  places  of 
attachment  of  the  eggs  (Hegner,  p.  213).    The  swimmerets  of  the  second  to 
fifth  abdominal  segments  are  very  similar  to  the  typical  appendage  already 
described.     The  sixth  pair  of  swimmerets,  called  the  uropods,  is  greatly  enlarged 
and  forms  with  the  telson  a  powerful  swimming  organ,  the  tail  fan.    Determine 
other  differences  between  the  uropods  and  the  other  swimmerets.    The  first 
pair  of  swimmerets  hi  the  female  lobster  and  crayfish  is  greatly  reduced  but 
otherwise  similar  to  the  others.     The  first  pair  of  swimmerets  in  the  male  lobster 
and  the  first  and  second  pairs  in  the  male  crayfish  are  modified  for  the  transference 
of  the  sperm  to  the  female.    They  consist  of  protopod  and  endopod  fused  into 
a  hard,  pointed,  grooved  structure.     Exopod  is  lacking,  except  in  the  second 
pair  of  the  crayfish,  where  it  appears  as  a  soft,  slender,  lateral  process. 

(2)  The  thoracic  appendages:  Remove  the  branchial  region  of  the  carapace 
from  the  left  side  by  lifting  it  up  and  cutting  away  the  free  portion.     The  branchial 
chamber  is  thus  exposed.     Observe  that  all  of  the  thoracic  appendages  have  gill- 
bearing  processes  extending  up  into  the  branchial  chamber.    The  thoracic 
appendages  comprise  five  pairs  of  walking  legs,  called  pereiopods,  and  three 
pairs  of  smaller  appendages,  called  maxillipeds,  anterior  to  them. 

Remove  completely  the  left  third  maxilliped,  the  appendage  just  in  front  of 
the  large  pincers.  Be  sure  to  get  the  gill-bearing  process  with  it.  Cut  through 
the  arthropodial  membrane  at  the  base  and  gently  detach  the  appendage.  The 
basal  joint,  the  coxopod,  of  the  third  maxilliped  bears  a  delicate,  hairy,  leaflike 
expansion,  the  epipod,  to  which  a  feathery  gill  is  attached.  Notice  the  great 
freedom  of  movement  of  the  coxopod  and  explain.  The  next  joint  distal  to  the 
coxopod  is  the  basipod.  From  it  arise  two  branches,  an  inner  endopod,  consisting 
of  five  joints,  and  an  outer  exopod,  of  many  small  joints.  The  maxilliped  is 
therefore  a  biramous  appendage,  similar  to  the  swimmeret,  but  showing  a  process 
of  reduction  of  the  exopod.  The  basal  joint  of  the  endopod  has  a  row  of  hard 
teeth,  used  in  crushing  food. 

Remove  the  left  second  pereiopod  with  all  of  its  parts  and  compare  with  the 
third  maxilliped,  placing  both  before  you  in  the  same  position.  The  pereiopod 
has  a  coxopod  with  an  epipod  and  gill,  a  basipod,  and  an  endopod  of  five  joints. 
The  comparison  shows,  however,  that  the  exopod  is  completely  lacking,  and  the 
pereiopod  is  therefore  a  uniramous  appendage.  Observe  the  pincer  at  the  end 
of  the  pereiopod  and  determine  how  it  arose. 


PHYLUM  ARTHROPODA 


109 


Examine  the  other  pereiopods,  comparing  them  with  the  second  one  and 
noting  differences.  Do  all  have  pincers,  epipods,  gills?  By  moving  the  legs, 
note  how  the  gills  are  moved.  In  what  directions  can  the  legs  be  moved  upon 
the  body?  In  what  directions  can  the  joints  of  the  leg  be  moved  upon 
each  other? 

The  first  pair  of  pereiopods  is  greatly  enlarged,  with  a  powerful  pincer,  or 
chela.  Note  that  the  two  chelae  of  the  lobster  are  not  alike,  but  one  is  massive 
with  broad  crushing  surfaces,  called  the  cracker  claw,  and  the  other  sharper  and 
more  slender,  with  little  teeth,  known  as  the  toothed  claw. 

On  the  inner  side  of  the  coxopod  of  the  third  pereiopods  of  the  female  find 
the  female  genital  openings.  The  male  genital  openings  are  in  the  same  place 
on  the  fifth  pereiopods. 

Draw  the  third  maxilliped  and  the  second  pereiopod  in  the  same  positions. 

Next  remove  the  left  second  maxilliped  complete.  Compare  with  the  third 
maxilliped.  Does  it  have  the  same  parts?  Notice  reduction  of  the  epipod  and 
gill  and  the  presence  of  only  four  joints  in  the  endopod. 

Remove  the  first  maxilliped,  and  compare  with  the  other  two.  Does  it  have 
an  epipod?  gill?  Observe  particularly  that  the  appendage  has  become  more 
broadened  and  leaflike.  This  is  due  to  the  moving  of  the  coxopod  and  basipod 
from  their  original  basal  position  to  form  the  medial  side  of  the  appendage.  The 
endopod  is  thus  shoved  laterally.  Endopod  and  exopod  of  the  first  maxilliped 
are  slender  processes  of  about  equal  size,  the  exopod  resting  in  a  groove  of  the 
endopod.  Endopod  is  thus  gradually  being  reduced,  consisting  now  of  but  two 
segments,  and  the  two  segments  of  the  protopod  are  being  gradually  broadened 
and  shifted  to  the  inside.  There  is  thus  produced  the  foliaceous  type  of 
appendage. 

The  thorax  therefore  has  eight  pairs  of  appendages,  the  three  pairs  of  maxil- 
lipeds  and  the  five  pairs  of  pereiopods,  and  consists  of  eight  segments. 

(3)  The  head  appendages:  The  head  has  five  pairs  of  appendages,  omitting 
the  eyes.  These  are,  beginning  with  the  most  posterior,  two  pairs  of  maxillae, 
a  pair  of  mandibles,  the  antennae,  and  the  antennules. 

Examine  the  second  maxilla  in  place.  Does  it  have  an  epipod?  gill?  Observe 
that  the  epipod  is  continuous  with  an  anterior  process,  which  is  the  exopod,  the 
whole  forming  an  elongated  blade,  pointed  at  both  ends,  which  fits  into  the 
anterior  end  of  the  branchial  chamber.  This  blade,  the  bailer  or  scaphognathite, 
moves  back  and  forth,  drawing  a  current  of  water  through  the  branchial  chamber 
over  the  gills  from  the  posterior  end  of  the  chamber  forward.  Within  the  exopod 
is  a  slender  endopod,  still  further  reduced  and  consisting  of  but  one  joint,  and 
within  this  the  expanded  protopod,  with  four  processes.  The  second  maxilla  is 
thus  decidedly  foliaceous.  Remove  it  and  draw. 

The  first  maxilla  is  a  reduced  foliaceous  appendage.  Its  two  inner  thin  plates 
are  the  protopod ;  the  outer  slender  process  is  the  endopod,  exopod  being  absent. 


no  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

Remove  the  first  maxilla.  The  small  process  in  front  of  it  is  not  considered  to  be 
an  appendage  but  is  a  part  of  the  lower  lip. 

The  heavy  mandible  is  now  exposed.  It  consists  of  a  single  triangular 
piece  with  strong  teeth  upon  its  inner  edge;  and  a  small  palp,  probably  the 
endopod,  folded  beneath  the  toothed  margin.  Spread  the  mandibles  apart  so 
as  to  see  the  mouth  opening.  In  front  of  the  mouth  opening  is  the  cushion-like 
upper  lip,  or  labrum. 

Examine  the  antenna.  In  the  middle  of  the  ventral  surface  of  its  basal 
segment  (coxopod)  find  the  renal  opening,  the  opening  of  the  excretory  organ. 
The  long  many-jointed  filament  is  the  endopod;  the  thin  sharp  projection  near 
the  base  of  the  filament  is  the  exopod.  Draw  the  antenna. 

The  antennule  or  first  antenna  has  a  protopod  of  three  joints  from  which 
arise  two  short  many-jointed  filaments,  which  are  probably  exopod  and  endopod. 

This  investigation  of  the  appendages  shows  that  there  are  at  least  five  seg- 
ments to  the  head,  eight  to  the  thorax,  and  six  to  the  abdomen,  or  nineteen 
appendage-bearing  segments.  If  the  telson  is  a  segment,  as  seems  reasonable, 
the  lobster  consists  of  twenty  segments.  Some  zoologists  believe  that  the  eyes 
also  represent  a  segment  and  raise  the  number  to  twenty-one,  but  considering 
that  eyes  occur  on  unsegmented  animals  it  seems  probable  that  they  are  not  a 
pair  of  appendages  homologous  to  the  others. 

/)  The  respiratory  system  and  the  branchial  chamber  (Hegner,  p.  204) :  Study 
the  arrangement  of  the  gills,  or  respiratory  organs,  in  the  left  branchial  chamber, 
where  they  have  already  been  exposed.  We  have  noted  that  one  gill  is  fastened 
to  the  epipod  of  most  of  the  thoracic  appendages.  Such  gills  fastened  to  append- 
ages are  called  podobranchiae.  Remove  the  podobranchia  and  epipod  from  the 
third  pereiopod,  and  observe  that  two  more  gills  are  situated  beneath  it  attached 
to  the  arthropodial  membrane.  These  are  arthrobranchiae.  In  the  lobster  there 
is  still  a  third  set  of  gills,  seen  by  removing  the  arthrobranchiae.  Under  the 
two  arthrobranchiae  note  a  gill  fastened  to  the  wall  of  the  thorax  and  hence 
called  a  pleurobranchia.  Each  thoracic  segment  has  therefore  typically  four 
gills,  but  not  all  of  them  possess  the  full  number,  as  the  student  may  readily 
discover.  The  crayfish  has  no  pleurobranchiae. 

Cut  off  one  of  the  gills  and  examine  its  structure.  It  consists  of  a  central 
axis  bearing  numerous  delicate  threadlike  filaments.  Examine  the  cut  surface 
of  the  axis  and  note  the  two  canals  which  it  contains,  one  for  blood  to  enter  the 
filaments,  the  afferent  vessel,  and  one  for  it  to  leave  the  filaments,  the  efferent 
vessel.  Note  the  hole  left  in  the  thoracic  wall  where  the  gill  was  removed  through 
which  the  blood  vessels  pass. 

Remove  all  the  gills  from  the  branchial  chamber  and  note  that  the  segmenta- 
tion of  the  thorax  is  now  visible.  Examine  the  region  where  the  extension  of  the 
carapace  over  the  branchial  chamber  was  cut  off  and  see  that  this  extension  was 


PHYLUM  ARTHROPODA  1 1 1 

not  really  the  sides  of  the  thorax  (which  are  concealed  by  the  gills)but  merely  a 
downward  fold  from  the  median  cardiac  region. 

g)  The  special  sense  organs:  These  are  best  studied  before  the  animal  is 
dissected.  The  body  and  appendages  of  the  lobster  bear  innumerable  hairs, 
many  of  which  are  sensory  hairs  attached  to  nerve  cells  and  having  tactile 
functions.  Many  hairs  upon  the  antennules,  antennae,  and  mouth  appendages 
are  also  organs  of  taste  and  general  chemical  sense.  The  head  appendages  are 
more  sensitive  than  the  others. 

The  eyes  of  the  lobster  are  compound  eyes,  i.e.,  they  are  made  up  of  a  large 
number  of  simple  eyes,  or  ommatidia,  which  are  radially  arranged.  The  cuticle 
covering  the  eye  is  thin,  transparent,  and  flexible,  lacking  the  calcareous  deposit. 
It  is  called  the  cornea.  Examine  it  with  the  hand  lens,  noting  the  minute  polyg- 
onal areas  of  which  it  is  composed.  Each  of  these  is  the  outer  end  of  one  of 
the  ommatidia.  Make  a  longitudinal  section  through  the  eye  and  eye  stalk 
with  a  sharp  knife  and  examine  the  cut  surface.  Observe  the  numerous  black 
ommatidia  radiating  from  a  central  white  region,  which  is  the  optic  ganglion. 
Read  Hegner  (pp.  205-8)  and  study  Fig.  103.  Then  remove  some  of  the  omma- 
tidia from  the  section  of  the  eye,  tease  on  a  slide  in  a  drop  of  water,  cover,  and 
examine.  You  should  be  able  to  identify  the  crystalline  cone,  the  rhabdome 
surrounded  by  black  pigment  cells,  and  the  nerve  fiber  leading  away  from  each 
ommatidium. 

The  statocyst,  or  organ  of  equilibrium,  is  a  thin  sac  located  in  the  basal  segment 
of  the  antennules.  Remove  an  antennule  and  cut  off  the  ventral  wall  of  the  basal 
segment  of  the  antennule.  This  reveals  a  thin-walled  sac  containing  sand  grains, 
attached  to  the  dorsal  wall  of  the  segment.  The  assistant  should  demonstrate 
the  crescent  of  sensory  hairs  within  the  sac  (read  Hegner,  p.  208). 

2.  The  internal  anatomy. — With  a  scissors  carefully  remove  piece  by  piece 
the  whole  dorsal  half  of  the  body  from  rostrum  to  telson,  beginning  at  the  anterior 
end.  In  doing  so  the  following  points  are  to  be  observed;  hence  read  the  next 
section  before  cutting.  Be  especially  careful  not  to  injure  the  blood  vessels, 
which  are  injected  with  a  yellow  fluid. 

a)  Body  wall  and  muscles:  Beneath  the  hard  exoskeleton  is  a  thin  membrane, 
the  epidermis,  which  is  the  ectoderm  and  secretes  the  exoskeleton.  Various 
muscles  will  be  found  attached  to  the  shell.  In  the  anterior  region  under  the 
carapace  is  the  large  thin-walled  stomach  from  the  anterior  and  posterior  ends 
of  which  gastric  muscles  extend  to  the  carapace.  At  the  sides  of  the  posterior 
end  of  the  stomach,  in  front  of  the  cervical  grooves,  is  a  heavy  fan-shaped  mass 
of  muscle.  This  is  the  mandibular  muscle,  which  moves  the  mandible.  In 
removing  the  dorsal  exoskeleton  of  the  abdominal  segments  notice  the  longi- 
tudinal muscles  attached  to  them  and  trace  them  forward  to  their  origins  on  the 
sides  of  the  thorax.  They  are  the  extensors  of  the  abdomen,  that  is,  they 


112  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

straighten  the  abdomen.  After  the  removal  of  the  whole  dorsal  exoskeleton, 
and  the  muscles  attached  to  them,  notice  the  large  masses  of  ventral  abdominal 
muscles,  the  flexors  of  the  abdomen.  Why  are  they  more  powerful  than  the 
extensors?  Remove  the  left  thoracic  wall,  and  observe  the  forward  extension 
of  the  flexor  muscles  to  their  origins  from  the  lateral  and  ventral  thoracic  walls. 

To  illustrate  the  arrangement  of  muscles  in  the  appendages,  examine  those 
of  the  chela.  Cut  off  the  chela  from  the  first  pereiopod  and  then  remove  the 
shell  from  one  surface  of  it.  Find  within  the  two  muscles,  one  much  larger  than 
the  other,  and  find  by  pulling  upon  them  their  method  of  attachment  and  action 
on  the  movable  part  of  the  pincer.  Pick  away  the  muscle  fibers  and  find  the 
strong  tendon  in  the  center  of  the  mass.  Each  joint  of  each  appendage  is  simi- 
larly provided  with  an  extensor  and  a  flexor  muscle  for  moving  the  next  joint 
(see  Hegner,  p.  209  and  Fig.  105). 

We  observe  that  the  muscular  system  of  the  lobster  is  highly  developed  as 
compared  with  that  of  the  lower  invertebrates  which  we  have  studied.  In  those 
forms  there  exist  simple  cylindrical  tubes  of  muscle  fibers,  extending  lengthwise, 
and  producing  merely  extension,  contraction,  or  bending  of  the  body.  But  in 
the  lobster  as  in  the  frog  separate  definite  muscles  exist  having  specific  actions 
on  various  parts  of  the  body,  permitting  much  greater  variety  and  exactness  of 
movement.  They  have  definite  origins  and  insertions  on  the  exoskeleton.  Are 
the  abdominal  muscles  segmentally  arranged? 

Place  a  small  piece  of  muscle  on  a  slide  in  a  drop  of  water,  tease  into  fibers, 
cover,  and  examine.  The  fibers  will  be  found  to  be  cross-striated,  like  the  volun- 
tary muscles  of  the  frog.  On  the  other  hand,  the  muscles  of  the  lower  inverte- 
brates are  like  the  smooth  involuntary  muscles  of  the  frog. 

b)  The  circulatory  system:  Your  specimen  should  now  have  the  dorsal  and 
one  lateral  wall  cleaned  away  so  as  to  expose  the  viscera.  The  conspicuous 
organs  are  the  stomach  anteriorly,  the  heart  posterior  to  this,  usually  injected 
with  yellow  material  and  with  yellow  vessels  springing  from  it,  and  a  large  white 
organ,  the  digestive  gland,  occupying  the  sides  of  the  space  within  the  thorax 
and  extending  back  into  the  abdomen. 

The  space  around  the  heart  and  between  the  viscera  is  not  a  coelome,  as  the 
student  might  expect,  but  it  is  an  enormous  blood  space,  or  blood  sinus,  filled 
in  life  by  blood.  The  coelome  has  been  greatly  reduced,  in  fact,  is  practically 
absent  through  this  great  development  of  blood  sinuses.  The  studies  which  we 
have  made  on  the  coelomes  of  the  earthworm  and  the  frog  should  convince  the 
student  that  this  space  in  the  lobster  cannot  be  a  coelome  because  mesenteries 
are  completely  lacking.  Note  that  none  of  the  organs  are  supported  by  mesen- 
teries and  that  there  is  no  peritoneal  lining. 

The  heart  lies  free  in  a  large  sinus,  the  pericardial  sinus.  The  following 
arteries  arise  from  it.  From  the  anterior  end  of  the  heart  in  the  median  line 
is  the  single  ophthalmic  artery.  Trace  it  forward  along  the  dorsal  surface  of  the 


PHYLUM  ARTHROPOD  A  113 

stomach  and  note  that  it  forks  to  supply  the  eyes.  On  each  side  of  the  ophthalmic 
artery  arises  an  antennary  artery  which  curves  downward  over  the  digestive 
gland.  Trace  it  and  note  its  branches  to  the  mandibular  muscle,  the  stomach, 
the  antennae,  and  the  antennules.  Directly  below  the  origin  of  the  antennary 
arteries  and  from  the  ventral  surface  of  the  heart  the  paired  hepatic  arteries 
extend  down  into  the  substance  of  the  digestive  gland.  From  the  posterior  end 
of  the  heart  a  large  vessel,  the  dorsal  abdominal  artery,  extends  backward  the 
whole  length  of  the  abdomen,  forking  in  the  sixth  abdominal  segment.  It  gives 
branches  to  the  intestine  which  is  immediately  beneath  it  and  to  the  extensor 
muscles  of  the  abdomen  which  have  been  removed.  Are  its  branches  segmentally 
arranged?  From  the  posterior  end  of  the  heart  at  the  same  point  as  the  origin 
of  the  dorsal  abdominal  artery,  another  large  artery,  the  sternal  artery,  arises 
and  proceeds  directly  ventrally.  Push  the  left  digestive  gland  carefully  aside 
to  see  it.  Its  further  course  will  be  traced  later. 

Make  an  outline  of  the  lobster  from  the  side  as  large  as  your  drawing  page 
and  in  this  put  the  heart  and  its  arteries.  Other  systems  will  be  added  to  this 
later. 

Remove  the  heart  from  the  body,  wash  it  in  water,  and  note  its  peculiar 
angled  form.  It  is  generally  somewhat  distorted  by  the  injection.  Find  the 
three  pairs  of  openings,  or  ostia,  in  the  wall  of  the  heart.  One  pair  is  on  the  dorsal 
surface,  one  pair  on  the  ventral  surface,  and  one  pair  is  lateral  just  under  the 
lateral  margins  (see  Hegner,  Fig.  101,  facing  p.  195). 

The  circulatory  system  of  the  lobster  and  other  arthropods  is  an  open  system, 
that  is,  the  only  definite  vessels  are  the  arteries,  and  the  circulation  is  completed 
through  open  spaces,  or  sinuses.  In  the  lobster  the  blood  passes  from  the  arteries 
into  these  sinuses  and  finally  collects  into  one  large  sinus,  the  sternal  sinus,  in 
the  median  ventral  line.  This  will  be  seen  later.  It  then  passes  into  the  gills 
by  the  afferent  vessels,  out  by  the  efferent  vessels,  already  seen  in  the  cross- 
section  of  a  gill,  and  back  to  the  pericardial  sinus  by  definite  channels.  When 
the  heart  expands  the  ostia  open  and  blood  is  sucked  into  the  heart  from  the 
pericardial  sinus.  The  blood  is  colorless. 

The  ophthalmic  artery,  heart,  and  dorsal  abdominal  artery  together  correspond 
to  the  dorsal  vessel  of  the  earthworm.  In  the  earthworm,  it  will  be  recalled,  the 
entire  dorsal  vessel  is  contractile,  but  in  the  lobster  the  power  of  contractility 
has  become  limited  to  one  region,  which  is  enlarged  and  now  designated  as  a 
heart.  There  is  also  in  the  lobster  a  vessel  to  be  seen  later  which  corresponds 
to  the  ventral  vessel  of  the  earthworm.  The  student  should  particularly  notice 
that  the  segmental  vessels,  connecting  these  two  in  each  segment  of  the  earth- 
worm, are  for  the  most  part  lacking  in  the  lobster. 

c)  The  reproductive  system:  Lying  under  the  heart  will  be  found  a  pair  of 
slender  gonads,  white  in  the  male,  pinkish  in  the  female.  They  extend  forward 
almost  to  the  anterior  end  of  the  stomach  and  posteriorly  beyond  the  termination 


ii4  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

of  the  digestive  gland,  in  the  lobster.  (In  the  crayfish  they  are  shorter  and 
broader,  and  the  posterior  part  is  single.)  The  two  gonads  have  a  slender  con- 
nection just  in  front  of  the  heart.  In  the  female  an  oviduct  will  be  found  arising 
from  each  ovary  in  the  region  of  the  heart.  Trace  it  downward  over  the  surface 
of  the  digestive  gland  into  the  third  leg.  In  the  male  the  vas  deferens  arises 
from  the  testis  in  the  same  region  and  extends  backward  to  the  fifth  leg.  Soon 
after  leaving  the  testis  the  vas  deferens  presents  a  bend,  then  widens  and  pro- 
ceeds straight  to  the  external  opening.  (The  vas  deferens  of  the  crayfish  is 
greatly  coiled.)  Draw  in  the  reproductive  system  in  your  lateral  view  of  the 
lobster. 

d)  The  digestive  system:  The  conspicuous  parts  of  the  digestive  system  are 
the  large  thin-walled  stomach  and  the  voluminous  digestive  gland.  The  latter, 
a  paired  white  organ  filling  the  greater  part  of  the  cavity  of  the  cephalothorax, 
is  often  called  a  "liver,"  but  as  it  really  combines  the  functions  of  both  a  liver 
and  a  pancreas  it  would  be  more  appropriately  designated  the  hepato-pancreas. 
Observe  the  lobes  and  small  tubules  of  which  it  is  composed.  Note  shape,  size, 
and  extent  of  the  digestive  gland  and  enter  it  on  your  drawing  with  very  light 
lines.  Then  remove  the  left  one  completely,  noting  as  you  do  so  the  place  where 
it  is  attached  to  the  posterior  end  of  the  stomach  by  an  hepatic  duct. 

The  removal  of  the  digestive  gland  exposes  the  stomach  more  fully.  Observe 
by  pushing  the  stomach  over  to  the  right  the  short  esophagus  connecting  it  with 
the  mouth.  The  stomach  is  divided  by  a  constriction  into  a  large  anterior  cardiac 
portion,  whose  wall  contains  hard  ossicles,  and  a  much  smaller  posterior  pyloric 
portion.  The  hepatic  ducts  open  into  the  pyloric  portion  just  above  the  rounded 
processes  which  project  downward  from  its  sides.  Fastened  to  each  side  of  the 
cardiac  portion  of  the  stomach  will  often  be  found  a  large  mass  of  crystals, 
calcareous  in  composition,  called  a  gastrolith.  See  Hegner  (p.  201)  for  its  pos- 
sible function.  From  the  end  of  the  pyloric  chamber  find  the  slender  intestine 
and  trace  it  to  the  anus.  It  makes  a  deep  ventral  bend  just  behind  the  stomach 
and  then  ascends  to  a  position  directly  beneath  the  dorsal  abdominal  artery.  In 
the  sixth  abdominal  segment  it  gives  off  a  blind  dorsal  sac,  or  caecum;  from  this 
point  to  the  anus  the  intestine  is  called  rectum.  Draw  in  these  parts  of  the  diges- 
tive system  on  your  outline  of  the  lobster. 

Remove  the  stomach,  leaving  the  esophagus  in  place.  Cut  it  open,  wash  it 
out,  and  examine  the  interior.  Note  the  hard  pieces,  or  ossicles,  in  the  walls 
of  the  cardiac  chamber,  the  paired  lateral  and  single  median  teeth,  and  the  pro- 
jecting processes  covered  with  fine  silky  hairs  in  the  posterior  division  of  the 
chamber,  blocking  the  passage  into  the  intestine.  The  teeth  and  ossicles  are  a 
grinding  apparatus,  called  the  gastric  mill,  operated  by  the  gastric  muscles 
attached  to  the  anterior  and  posterior  ends  of  the  stomach;  the  hairy  processes, 
a  straining  apparatus,  preventing  the  coarser  particles  from  passing  into  the 
intestine.  Make  a  drawing  showing  the  interior  of  the  stomach. 


PHYLUM  ARTHROPOD  A  115 

e)  The  excretory  system:  In  the  anterior  end  of  the  cephalic  cavity,  inside 
of  the  base  of  the  antenna,  locate  a  circular  greenish  mass,  liberally  supplied  by 
branches  of  the  antennary  artery.  This  is  the  excretory  organ,  commonly 
called  "  green  gland."  It  is  in  reality  a  modified  nephridium,  which  has  lost 
its  funnel-shaped  opening  into  the  coelome  (since  there  is  no  coelome).  By 
carefully  spreading  it  out  with  a  forceps,  determine  that  it  is  a  blind  sac,  curved 
upon  itself  into  a  circle.  The  renal  opening  in  the  basal  joint  of  the  antenna 
has  already  been  observed.  The  student  should  note  that  while  in  the  annelids 
there  is  a  pair  of  such  nephridia  in  practically  every  segment,  in  the  lobster  the} 
are  present  in  one  segment  only,  the  antennary  segment.  This  is  anothei 
example  of  the  loss  of  segmental  structures,  which  characterizes  the  arthropods 
as  compared  with  the  annelids.  Draw  in  the  green  gland  on  your  side  view. 

/)  The  nervous  system:  Remove  all  soft  parts  from  the  interior,  leaving  the 
esophagus  and  sternal  artery  in  place.  First  begin  in  the  abdomen  and  care- 
fully remove  all  of  the  ventral  abdominal  muscles,  noting  their  segmental  arrange- 
ment and  the  complex  manner  in  which  they  loop  over  one  another.  In  the 
median  ventral  line  of  the  abdomen,  next  to  the  inner  surface  of  the  shell,  is  a 
white  cord,  the  ventral  nerve  cord.  In  the  thoracic  region  this  will  be  found 
to  disappear  into  a  cavity  which  is  roofed  over  by  hard  plates.  Clean  out  the 
muscles  and  other  soft  parts  in  the  thorax  until  you  have  exposed  these  plates. 
They  form  an  internal  skeleton,  called  the  endophragmal  skeleton;  this  is  really 
produced  by  ingrowth  from  the  exoskeleton. 

The  cavity  underneath  the  endophragmal  skeleton  is  the  sternal  sinus,  which 
was  mentioned  in  connection  with  the  circulatory  system  as  the  large  sinus  in 
which  all  of  the  venous  blood  collects  before  going  to  the  gills.  In  this  sinus 
are  also  located  the  nerve  cord  and  the  branches  of  the  sternal  artery.  Remove 
the  endophragmal  skeleton  by  cutting  along  each  side  and  taking  out  the  middle 
piece,  and  trace  the  nerve  cord  forward  in  the  sternal  sinus  to  the  esophagus. 
Here  note  that  it  forks,  passing  on  each  side  of  the  esophagus  and  uniting  again 
into  a  bilobed  mass  just  within  the  region  occupied  by  the  eyes. 

The  bilobed  mass  beneath  the  eyes  is  the  so-called  brain,  better  designated 
as  the  supra-esophageal  ganglia.  It  consists  of  two  ganglionic  masses  fused 
medially,  and  sends  nerves  to  the  eyes  (where  they  expand  into  the  optic  ganglia, 
situated  in  the  eye  stalks),  the  antennules,  and  the  antennae.  The  brain,  there- 
fore, represents  at  least  three  pairs  of  ganglia  fused  together.  From  the  brain 
arise  the  two  circum-esophageal  commissures.  Trace  these  around  the  esophagus 
to  the  large  sub-esophageal  ganglion,  just  behind  the  esophagus.  Note  branches 
arising  from  the  circum-esophageal  commissures  and  sub-esophageal  ganglion. 
Trace  the  nerve  cord  posteriorly  along  the  floor  of  the  thorax,  noting  the  enlarge- 
ments or  ganglia.  Behind  the  sub-esophageal  ganglion  there  are  three  ganglia; 
then  the  nerve  cord  forks  to  allow  the  sternal  artery  to  pass  through;  behind  the 
sternal  artery  are  two  more  thoracic  ganglia.  Since  in  a  segmented  animal 


n6  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

there  is  a  ganglion  (really  a  pair)  to  each  segment,  how  many  ganglia  should 
there  be  in  the  cephalothorax  of  the  lobster?  Since  the  brain  supplies  the  first 
two  pairs  of  appendages,  how  many  appendages  must  be  supplied  by  the  sub- 
esophageal  ganglion,  and  of  how  many  fused  ganglia  does  it,  therefore,  consist? 

Trace  the  nerve  cord  back  into  the  abdomen.  Is  there  a  ganglion  for  each 
segment ?  Does  the  telson  have  a  ganglion?  Note  the  branches  of  the  abdominal 
nerve  cord. 

Observe  the  branches  of  the  sternal  artery  under  the  ventral  nerve  cord.  It 
passes  between  the  two  halves  of  the  nerve  cord,  between  the  fourth  and  fifth 
thoracic  ganglia,  and  promptly  divides  into  an  anterior  horizontal  branch,  the 
ventral  thoracic  artery,  and  a  posterior  branch,  the  ventral  abdominal  artery. 
These  correspond  to  the  ventral  vessel  of  the  earthworm. 

Put  in  the  nerve  cord  and  its  ganglia  accurately,  and  the  branches  of  the 
sternal  artery  on  your  drawing.  The  drawing  is  now  complete. 

The  nervous  system  of  the  lobster  is  very  much  like  that  of  the  earthworm, 
except  that  as  in  the  case  of  the  other  systems  of  the  lobster  it  shows  a  partial 
loss  of  the  segmental  arrangement  through  fusion.  The  nervous  system  of 
both  earthworm  and  lobster  is  based  upon  the  same  plan  as  that  of  Planaria, 
consisting  fundamentally  of  two  ventral  ganglionated  cords  arising  from  a  dorsal 
brain.  This  type  of  nervous  system  is  common  to  all  the  invertebrates  (except 
those  having  radial  symmetry)  and  is  called  the  ladder  type.  The  ventral  cords, 
originally  separated  rather  widely,  come  together  in  the  segmented  animals  to 
produce  an  (apparently)  single  cord. 

3.  General  considerations  on  the  lobster. — The  chief  principle  which  we 
wish  to  bring  out  through  the  study  of  the  anatomy  of  the  lobster  has  already 
been  emphasized  throughout  the  laboratory  instructions.  It  is  that  the  lobster, 
although  a  segmented  animal  like  the  annelids,  exhibits  a  marked  tendency  to 
an  obliteration  of  the  segmentation,  through  fusion  and  loss  of  segments  and  of 
segmented  structures.  This  tendency  is  still  further  in  evidence  in  the  verte- 
brates where  dissection  alone  reveals  that  the  frog  is  segmented,  and  then  in 
only  a  few  systems.  What  systems  of  the  lobster  are  segmented?  Which  is 
the  most  completely  segmented?  In  what  part  of  the  body  is  the  segmentation 
most  complete?  Where  it  is  most  obscure?  Compare  with  the  frog  and  deter- 
mine wh  ner  the  systems  and  the  part  of  the  body  which  exhibit  the  greatest 
degree  o  segmentation  are  the  same  in  the  two  animals.  Is  it  the  same  system 
in  the  two  which  retains  the  most  primitive  segmentation?  What  is  the  signifi- 
cance of  this  fact?  Does  the  lobster  have  all  the  systems  which  are  present 
in  the  frog?  What  one  does  it  possess  which  the  earthworm  lacked?  Why  is 
this  system  the  last  to  appear  in  the  animal  series?  Are  the  systems  which  the 
earthworm  and  the  lobster  have  in  common  better  developed  and  more  specialized 
in  the  latter?  Which  one  differs  the  least  from  that  of  the  earthworm?  Do  the 
systems  of  the  lobster  compare  favorably  with  those  of  the  frog  as  to  specializa- 


PHYLUM  ARTHROPOD  A  117 

tion  for  particular  functions?  What  system  of  the  lobster  has  made  the  least 
progress?  Do  both  the  lobster  and  the  frog  seemed  to  have  attained  a  fairly 
high  degree  of  adjustment  (adaptation)  to  the  conditions  under  which  each 
lives? 

B.      THE  ANATOMY   OF   THE   GRASSHOPPER 

The  grasshopper  is  selected  as  a  representative  of  the  great  group  of  insects 
because  it  is  relatively  large,  easily  obtained,  and  a  rather  generalized  form.  The 
following  description  is  based  upon  the  large  Florida  grasshoppers. 

i.  External  anatomy. — Obtain  a  preserved  specimen.  Compare  with  the 
earthworm  and  especially  with  the  lobster.  Is  the  animal  bilaterally  sym- 
metrical? Is  it  segmented  throughout?  In  what  part  of  the  body  is  the  segmen- 
tation most  apparent?  least  apparent?  Does  it  have  jointed  appendages  like 
the  lobster?  Do  they  occur  on  every  segment?  What  part  of  the  body  lacks 
them?  Is  this  in  accordance  with  the  principle  of  specialization  of  anterior 
regions,  which  we  observed  in  the  other  animals  studied?  Does  the  animal  have 
a  definite  color  pattern  ? 

The  body  is  covered  by  a  chitinous  exoskeleton,  similar  to  that  of  the  earth- 
worm and  the  lobster.  It  is  secreted  by  the  ectoderm,  or  epidermis,  which  lies 
beneath  it.  As  in  the  lobster  it  consists  of  hard  regions,  or  sclerites,  joined 
together  by  thin  membranes,  the  arthropodial  membranes,  at  lines  known  as 
sutures. 

The  body  is  divided  into  head,  thorax,  and  abdomen.  Are  these  regions 
more  distinctly  separated  than  in  the  lobster?  Each  part  consists  of  a  definite 
number  of  segments.  Each  segment  as  in  the  lobster  is  typically  composed  of  a 
dorsal  sclerite,  the  tergum  (commonly  called  notum  in  insects),  a  lateral  sclerite, 
the  pleuron,  and  a  ventral  sclerite,  the  sternum. 

a)  The  head  and  its  appendages:  Is  the  head  readily  movable  upon  the  body? 
The  head  shows  no  segmentation.  The  larger  part  of  it  is  inclosed  in  one  hard 
sclerite,  the  epicranium,  in  which  may  be  distinguished  a  top  (vertex),  sides 
(genae),  and  a  front  (frons).  Looking  at  the  head  from  in  front,  the  lowei 
limit  of  the  frons  is  marked  by  a  distinct  transverse  suture.  Below  this  suture 
is  a  rectangular  sclerite,  the  clypeus,  and  below  this  and  attached  to  it  another 
sclerite,  the  bilobed  upper  lip  or  labrum.  Observe  that  the  labrum  movable; 
it  is  not,  however,  an  appendage. 

The  head  bears  eyes,  antennae,  and  three  pairs  of  mouth  parts,  f  here  is  a 
pair  of  large  compound  eyes  situated  in  the  upper  parts  of  the  genae.  Examine 
them  with  the  hand  lens  and  note  the  minute  hexagonal  areas  into  which  the 
surface  is  divided.  Each  of  these  is  the  outer  end  of  an  ommatidium,  and  the 
structure  of  th'j  compound  eye  is  the  same  as  in  the  lobster.  The  grasshopper 
also  has  three  simple  eyes,  or  ocelli,  one  anterior  to  the  dorsal  portion  of  each 
compound  eye  on  the  ridge  which  separates  frons  and  gena,  and  the  third  in 

10 


ii8  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

the  depression  between  the  two  ridges  in  the  median  line  of  the  frons.  For  the 
structure  of  the  ocelli  see  Hegner  (p.  245).  Draw  a  front  view  of  the  head. 

The  antennae  are  the  first  pair  of  head  appendages.  They  are  jointed  fila- 
mentous structures,  springing  from  depressions  in  the  upper  part  of  the  frons. 
The  antennae  are  very  important  olfactory  and  tactile  appendages.  Remove 
an  antenna  and  examine  with  the  low  power,  noting  the  sensory  hairs  upon  it. 

With  the  forceps,  remove  the  clypeus  and  labrum  in  one  piece,  and  examine 
the  under  surface.  This  forms  the  roof  of  the  mouth  and  bears  a  central  club- 
shaped  elevation,  the  epipharynx,  probably  of  sensory  function. 

The  removal  of  the  labrum  exposes  the  three  pairs  of  mouth  parts.  The  first 
of  these,  constituting  the  second  pair  of  head  appendages,  is  the  mandibles,  very 
hard  brown  organs  with  toothed  inner  edges.  Remove  these  and  draw  one 
under  a  hand  lens.  The  next  pair  of  mouth  parts,  the  third  pair  of  head  append- 
ages, are  the  maxillae  (first  maxillae).  They  are  lateral  and  each  has  a  con- 
spicuous process,  the  palp.  Remove  a  maxilla  complete  and  study  it  with  the 
hand  lens.  It  consists  of  a  basal  portion,  composed  of  two  segments,  a  lower 
car  do  and  an  upper  stipes,  from  which  springs  three  processes.  The  inner  one 
is  a  curved,  toothed  blade,  the  lacinia;  the  middle  one  an  oval  plate,  the  galea, 
composed  of  two  joints;  and  the  outer,  a  slender  jointed  process,  the  maxillary 
palp,  supported  by  a  small  basal  joint,  the  palpifer.  Draw  the  maxilla.  It  is 
probable  that  the  palp  is  the  endopod,  and  the  remainder  of  the  appendage  the 
protopod,  exopod  being  absent. 

The  last  pair  of  mouth  parts,  the  fourth  pair  of  head  appendages,  is  the  labium, 
or  lower  lip,  lying  below  the  mouth  in  the  median  line.  It  is  composed  of  two 
maxillae  (the  second  maxillae)  partially  fused  in  the  median  line.  Attached 
to  the  labium  and  projecting  inward  from  it  to  form  the  floor  of  the  mouth  cavity 
is  an  elevation,  the  hypopharynx,  which  serves  as  an  organ  of  taste.  Remove 
the  labium  completely  and  identify  the  following  parts  with  the  hand  lens:  the 
basal  crescentic  segment,  the  submentum;  the  next  single  piece,  the  mentum; 
the  paired  labial  palps,  springing  from  the  sides  of  the  mentum  through  a  small 
joint,  the  palpifer;  and  the  paired  flat  median  plates,  the  ligulae.  Draw  the 
labium. 

Since  the  head  bears  four  pairs  of  appendages  it  must  consist  of  at  least  four 
segments.  Investigation  of  insect  embryos  has  shown  that  there  is  another 
segment  in  front  of  the  one  bearing  the  antennae,  and  still  another  between  the 
antennary  and  mandibular  segments.  There  are  thus  six  segments  in  the  insect 
head.  The  antennae  of  the  insects  correspond  to  the  antennules  of  the  lobster; 
while  the  segment  and  the  appendages  which  correspond  to  the  antennae  of  the 
lobster  are  lost  in  the  adult  insect. 

b)  The  thorax  and  its  appendages:  The  thorax  is  composed  of  three  stout 
segments,  called  the  prothorax,  mesothorax,  and  metathorax,  respectively,  begin- 
ning at  the  anterior  end.  The  tergum,  or  no  turn,  called  the  pronotum,  of  the 


PHYLUM  ARTHROPOD  A  119 

prothorax  is  greatly  enlarged  and  extends  back  like  a  shield  over  the  other  two 
segments  of  the  thorax.  It  is  also  seen  to  be  composed  of  four  distinct  sclerites, 
one  behind  the  other.  The  sternum  of  the  prothorax  has  a  sharp  posteriorly 
directed  spine;  the  pleuron  is  rudimentary.  The  prothorax  bears  the  first  pair 
of  legs.  Is  the  prothorax  independently  movable? 

Cut  away  the  backward  extension  of  the  pronotum.  In  the  middle  of  the 
side,  in  the  membrane  between  the  prothorax  and  mesothorax,  find  an  oval 
opening.  This  is  a  spiracle,  or  stigma,  one  of  the  openings  into  the  respiratory 
system.  In  the  mesothorax,  identify  the  dorsal  tergum,  or  notum,  the  lateral 
pleuron,  the  ventral  broad  sternum.  Both  tergum  and  pleuron  are  composed 
of  more  than  one  sclerite.  The  mesothorax  bears  dorsal  outgrowths,  the  first 
pair  of  wings,  and  a  ventral  pair  of  appendages,  the  second  pair  of  legs.  Cut 
off  the  wings. 

The  metathorax  is  similar  in  form  and  parts  to  the  mesothorax  and  bears  the 
second  pair  of  wings  and  third  pair  of  legs.  Cut  off  the  wings.  Locate  another 
spiracle  between  the  ventral  portions  of  the  pleura  of  the  mesothorax  and 
metathorax. 

Examine  the  wings.  Compare  them  as  to  form,  size,  color,  thickness.  What 
do  you  consider  to  be  the  functions  of  each  pair?  The  wings  arise  as  saclike 
outgrowths  of  the  body  wall.  During  development  the  two  walls  of  the  sac 
become  pressed  together,  forming  a  thin  membrane.  The  veins  or  nerves  of  the 
wings  are  respiratory  tubes,  filled  with  air,  each  surrounded  by  a  tubular  blood 
sinus.  After  the  insect  attains  its  adult  size,  blood  ceases  to  flow  in  the  wings, 
and  they  become  dry,  hard,  and  lifeless.  Examine  a  piece  of  the  second  pair  of 
wings  under  the  microscope,  and  note  the  air  tube,  or  tracheal  tube,  and  the  blood 
sinus  around  it  in  each  of  the  veins. 

Remove  a  leg  from  the  body  noting  the  depression  in  the  body  where  it  fits, 
the  arthropodial  membrane  which  attaches  it  to  the  body,  and  the  muscles  at 
its  base.  It  is  composed  of  five  segments.  The  rounded  segment  which  adjoins 
the  body  is  the  coxa.  It  is  succeeded  by  a  quite  small  joint,  the  trochanter.  The 
next  segment  is  the  long  powerful  femur.  Beyond  this  comes  the  more  slender, 
spiny  tibia.  The  terminal  part  of  the  leg  is  the  tarsus,  consisting  of  three  joints, 
and  with  five  ventral  pads,  the  pulvilli,  and  a  terminal  pair  of  hooks.  Compare 
the  three  legs  of  the  grasshopper  with  each  other.  Do  all  have  the  same  parts? 
Can  you  associate  differences  in  relative  proportions  of  parts  with  differences  in 
function?  Are  the  legs  well  "adapted"  for  their  functions?  What  are  the  uses 
of  the  pulvilli  and  terminal  hooks? 

c)  The  abdomen  and  its  appendages:  Each  abdominal  segment  consists  of  a 
tergum,  a  U-shaped  piece  forming  the  dorsal  and  lateral  walls,  and  a  sternum, 
the  convex  ventral  plate.  The  pleuron  is  practically  lacking  but  is  represented 
by  the  membranous  fold  where  tergum  and  sternum  articulate.  Just  above  this 
line  of  junction,  on  the  lower  border  of  the  tergum  will  be  found  a  spiracle,  or 


120  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

stigma.  How  many  pairs  of  stigmata  are  there  on  the  abdomen?  The  tergum 
and  sternum  of  the  first  abdominal  segment  are  separated  from  each  other  by 
the  depression  for  the  insertion  of  the  third  legs.  The  sternum  is  fused  to  the 
sternum  of  the  metathorax,  a  crescentic  suture,  however,  marking  the  boundaries 
between  them.  The  tergum  bears  upon  its  sides  a  circular  opening  with  a 
chitinous  run  across  which  is  stretched  a  thin  membrane.  This  is  the  organ 
of  hearing,  or  chordotonal  organ,  commonly  called  an  "ear."  On  the  anterior 
border  of  the  ear  is  the  first  abdominal  spiracle. 

The  next  seven  abdominal  segments  are  all  alike  and  present  no  new  features. 
The  remainder  of  the  abdomen  is  different  in  form  and  structure  in  the  two  sexes. 
In  both  sexes,  the  ninth  and  tenth  terga  are  narrow  and  more  or  less  fused.  From 
the  tenth  tergum  a  broad  triangular  plate,  the  suranal  plate,  extends  posteriorly, 
forming  the  roof  of  the  anal  opening.  Whether  the  suranal  plate  is  a  part  of  the 
tenth  tergum  or  represents  an  eleventh  tergum  is  undecided.  From  the  sides 
of  the  tenth  tergum  a  pair  of  small  pointed  processes  projects  posteriorly.  These 
are  called  the  cerci  or  cercopods,  and  are  generally  regarded  as  the  appendages 
of  the  tenth  segment.  Under  each  cercus  is  a  larger  triangular  plate,  the  podical 
plate,  supposed  by  many  authors  to  represent  part  of  an  eleventh  segment.  The 
anal  opening  is  between  the  two  podical  plates. 

In  the  male  there  is  a  broad  ninth  sternum,  followed  by  a  triangular  plate 
curving  dorsally,  called  the  subgenital  plate,  probably  representing  the  tenth 
sternum.  The  subgenital  plate  terminates  dorsally  in  two  short  spines. 
Between  the  subgenital  plate  and  the  podical  plates  is  the  male  genital  opening, 
and  the  male  genital  apparatus  is  concealed  under  the  subgenital  plate,  which 
forms  a  kind  of  hood  over  it.  Grasp  the  subgenital  plate  and  pull  it  backward, 
revealing  the  male  apparatus  ending  in  a  hard  point,  the  penis. 

In  the  female,  the  abdomen  ends  ventrally  with  the  eighth  sternum,  from 
which  a  pointed  projection,  the  egg  guide,  extends  posteriorly.  Behind  the 
eighth  sternum,  terminating  the  body,  are  two  pairs  of  hard  pointed  styles,  which 
together  constitute  the  ovipositor,  or  egg-depositing  apparatus.  The  female 
genital  opening  lies  at  the  base  of  the  egg  guide,  and  will  be  seen  later.  There 
is  no  doubt  that  the  styles  of  the  ovipositor  are  true  abdominal  appendages, 
homologous  with  the  legs  and  mouth  parts.  The  grasshopper  lays  its  eggs  in 
the  ground.  Does  this  fact  suggest  to  you  the  function  of  the  styles? 

2.  The  internal  anatomy. — The  dissection  of  preserved  specimens  is  rather 
unsatisfactory.  For  this  reason  the  student  may  have  some  difficulty  in  locating 
all  of  the  parts  described  and  should  not  waste  too  much  time  in  searching  for 
them. 

Cut  out  the  dorsal  body  wall  in  one  strip  beginning  in  front  of  the  suranal 
plate  and  extending  forward  to  the  compound  eyes.  Remove  and  preserve 
the  strip  without  injuring  it.  A  large  space  containing  the  viscera  is  revealed. 
As  in  the  case  of  the  lobster,  this  space  is  not  a  coelome  but  is  an  enormous  blood 


PHYLUM  ARTHROPOD  A  121 

sinus;  this  is  evidenced  by  the  complete  lack  of  mesenteries.  The  coelome  is 
in  fact  practically  entirely  wanting  in  insects.  A  yellowish  material,  the  fat 
body,  representing  stored  food,  will  be  found  attached  to  the  viscera  and  body 
wall.  Note  also  the  slender  bandlike  muscles  originating  on  the  body  wall  and 
attached  to  the  movable  appendages. 

Place  the  specimen  in  a  wax-bottomed  dissecting  pan,  pin  it  down  by  pins 
through  the  wall,  and  fill  the  pan  with  water. 

a)  The  respiratory  system:  There  is  perhaps  no  other  system  to  be  found  in 
the  animal  kingdom  which  so  excites  the  admiration  of  the  zoologist  as  the  respira- 
tory system  of  the  insects.     Unfortunately  it  is  impossible  to  study  it  satis- 
factorily in  preserved  material.     It  consists  of  a  series  of  tubes,  symmetrically 
and  segmentally  arranged,  called  the  tracheal  tubes,  or  tracheae.    These  open 
to  the  exterior  through  the  spiracles,  or  stigmata,  which  have  already  been  noted 
on  the  surface  of  the  body.     To  see  the  tracheal  tubes,  push  the  viscera  of  the 
grasshopper  gently  to  one  side  and  look  on  the  inside  of  the  body  wall  opposite 
the  points  where  the  spiracles  are  situated.    A  white  tube  will  be  seen  extending 
inward  from  each  spiracle.    With  a  little  practice  one  will  soon  be  able  to  identify 
similar  tubes  throughout  the  body.     Note  also  particularly  in  the  thorax  the 
large  white  air  sacs,  which  are  connected  with  the  tracheae  and  serve  to  increase 
the  capacity  of  the  tracheal  system.    The  tracheal  system  of  the  grasshopper 
consists  of  three  pairs  of  longitudinal  trunks,  connected  by  segmental  branches, 
giving  off  branches  to  all  parts  of  the  body  and  provided  in  certain  places  with 
air  sacs.     Recall  the  tracheal  system  seen  in  the  fly  larvae  (Section  II,  F,  3),  and 
examine  Hegner's  Figs.  135  (p.  243)  and  137  (p.  244). 

Remove  a  piece  of  a  tracheal  tube,  mount  in  a  drop  of  water  on  a  slide,  and 
examine  with  the  microscope.  Observe  the  spiral  thread  on  the  inside  of  the 
tracheal  tube.  What  is  its  function?  Draw. 

The  tracheae  are  tubes  produced  by  ingrowth  of  the  ectoderm  and  lined 
therefore  by  the  same  chitinous  layer  which  covers  the  body,  in  which  the  spiral 
threads  arise  by  local  thickenings.  The  tracheae  arise  therefore  in  a  manner 
opposite  to  that  of  gills,  which  are  outgrowths  of  the  body  wall.  Both  serve  the 
same  purpose,  an  increase  of  surface.  But  while  gills  contain  blood  which 
obtains  oxygen  through  their  thin  walls,  the  tracheal  tubes  are  filled  with  air. 
The  finest  ramifications  of  the  tracheal  tubes  are  in  contact  with  single  cells; 
and  further,  the  blood  in  the  large  blood  sinuses  is  in  contact  with  the  walls  of 
the  tracheae.  Thus  oxygen  is  brought  directly  in  contact  with  all  parts  of  the 
body,  even  the  smallest;  and  a  respiratory  system  which  is  regarded  as  the  most 
efficient  among  animals  results.  The  air  in  the  tracheal  system  is  changed 
through  respiratory  movements  of  the  body. 

b)  The  circulatory  system:  Associated  with  the  development  of  a  remarkably 
efficient  respiratory  system,  there  is  a  correspondingly  poor  differentiation  of  the 
circulatory  system.     There  is  a  long  segmented  heart  situated  in  the  median 


122  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

dorsal  line  of  the  abdomen.  Look  on  the  underside  of  the  dorsal  strip  removed 
from  the  animal  for  a  long  tubular  structure  with  several  dilatations.  It  is 
often  indistinguishable  in  specimens  which  have  been  preserved  for  a  long  time. 
Fan-shaped  muscles  are  attached  on  either  side  to  each  dilatation;  they  are  called 
the  alary  muscles  and  are  supposed  to  help  dilate  the  heart.  The  wall  of  the 
heart  is  pierced  with  ostia,  as  in  the  lobster,  through  which  it  sucks  in  blood 
from  the  great  blood  sinus  which  surrounds  it. 

There  are  no  arteries  or  other  blood  vessels,  but  the  blood  flows  out  from  the 
anterior  open  end  of  the  heart  into  the  sinuses. 

c)  The  reproductive  system:  This  system  will  be  considered  first  since  it  is 
the  first  system  noticeable  on  looking  into  the  cavity  of  the  abdomen.  In  the 
male  the  testis  forms  a  white  mass  in  the  posterior  end  of  the  animal  dorsal  to 
the  intestine.  From  each  side  of  the  ventral  surface  of  this  mass  a  male  duct 
or  vas  deferens  arises  and  passes  posteriorly  and  ventrally  to  the  end  of  the 
abdomen  where  it  is  joined  by  a  mass  of  tubules,  the  accessory  glands,  located  in 
the  seventh  and  eighth  abdominal  segments.  The  lateral  walls  of  these  segments 
should  be  removed  to  see  these  tubules.  The  two  vasa  deferentia  then  unite  in 
the  ventral  median  line  within  the  eighth  sternum  to  a  single  duct  which  passes 
into  a  muscular  mass  surrounding  the  base  of  the  copulatory  organ,  or  penis. 
Remove  the  ninth  sternum  and  the  subgenital  plate  and  look  for  these  parts. 
Remove  the  muscles  from  the  penis  and  note  with  a  hand  lens  or  microscope 
the  four  hard  chitinous  styles  which  compose  it. 

In  the  female  the  two  ovaries  are  situated  in  the  posterior  end  of  the  abdomen, 
one  on  each  side  of  the  digestive  tract.  Each  consists  of  a  number  of  parallel 
ovarian  tubes,  more  (or  less  vertical  in  position,  resting,  so  to  speak,  in  a  row  upon 
the  oviduct,  which  arises  from  their  ventral  ends.  In  each  ovarian  tube  is  a  row 
of  eggs,  of  which  the  largest  ones,  often  plainly  visible  as  oval  brown  bodies,  are 
placed  nearest  the  beginning  of  the  oviduct.  The  two  oviducts  pass  posteriorly 
and  ventrally  and  unite  in  the  median  ventral  line  under  the  intestine  to  a  com- 
mon duct,  the  vagina.  The  vagina  opens  to  the  exterior  by  the  female  genital 
opening  located  at  the  base  of  the  egg  guide.  Grasp  the  egg  guide  with  a  forceps 
and  pull  it  forcibly  out  of  its  position  between  the  ventral  styles  of  the  ovipositor. 
At  its  base  note  a  little  cushion  which  folds  over  the  genital  opening  and  must 
be  pulled  back  to  reveal  the  latter.  Remove  the  eighth  sternum  and  locate 
within  it  the  vagina,  a  broad  tube  passing  to  the  genital  opening.  Lift  out  the 
vagina  and  note  just  above  it  another  tube,  the  copulatory  sac,  which  receives 
the  sperm  of  the  male  in  copulation.  This  opens  to  the  exterior  just  dorsal  to 
the  vagina.  Attached  to  the  copulatory  sac  is  a  slender  duct  leading  from  a 
small  body  located  just  above  the  point  where  the  two  oviducts  unite  to  form 
the  vagina.  This  body  is  the  cement  gland.  In  laying  eggs  the  grasshopper  digs 
a  hole  in  the  ground  with  the  ovipositor;  the  eggs  are  then  passed  out  through 


PHYLUM  ARTHROPODA  123 

the  genital  opening,  receiving  sperm  from  the  copulatory  sac  and  being  stuck 
together  into  packets  by  a  fluid  from  the  cement  gland.  The  egg  guide  directs 
the  eggs  in  their  passage  to  the  exterior. 

Draw  from  the  side  the  parts  of  the  reproductive  system  which  you  have 
been  able  to  find. 

d)  The  digestive  system:  The  larger  part  of  the  internal  cavity  is  filled  with 
the  digestive  tract.     Remove  the  reproductive  system.     Clean  away  the  fat 
body  and  cut  off  one  lateral  side  of  the  abdomen  and  thorax  and  the  same  side 
of  the  head.     Identify  the  short  esophagus  extending  inward  from  the  mouth 
and  opening  into  a  large  crop  which  fills  most  of  the  cavity  of  the  thorax.     Behind 
the  crop  is  the  elongated  stomach,  or  ventriculus,  partially  concealed  by  six  thin- 
walled  gastric  caecae.     Each  gastric  caecum  is  attached  by  its  middle  portion 
to  the  wall  of  the  stomach  so  that  one  of  its  pointed  ends  projects  forward  and 
the  other  backward  from  the  point  of  attachment.    The  anterior  part  of  the 
stomach,  covered  by  the  caecae  is  distinguished  as  the  proventriculus  or  gizzard, 
but  it  is  not  well  differentiated  in  the  grasshopper.    The  posterior  end  of  the 
stomach  is  marked  by  the  presence  of  a  tangle  of  threads,  the  Matpighian 
tubules.     Beyond  this  region  is  the  intestine,  at  first  wide,  then  presenting  a 
short  narrow  portion,  the  colon,  then  widening  into  a  rectum,  which  extends  to 
the  anus.    The  rectum  frequently  contains  a  cylindrical  pellet  of  faeces.    Its 
surface  is  marked  off  by  longitudinal  muscle  bands  into  six  expanded  areas, 
known  as  the  rectal  glands.    The  position  of  the  anus  under  the  suranal  plate 
has  already  been  noted.     Look  in  the  sides  of  the  thorax  among  the  muscles  and 
fat  body  for  the  salivary  glands,  a  cluster  of  small  round  glands  attached  to  a 
duct.     The  ducts  open  into  the  mouth. 

Draw  an  outline  of  the  animal  from  the  side  and  put  in  the  parts  of  the 
digestive  tract.  Other  systems  which  the  student  has  seen  well  enough  may  also 
be  entered  upon  the  drawing. 

e)  The  excretory  system:   The  threadlike  Malpighian  tubules  arising  at  the 
junction  of  the  stomach  and  intestine  are  the  excretory  organs.    They  are  out- 
growths of  the  digestive  tract  and  are  therefore  entirely  distinct  morphologically 
from  the  excretory  organs  of  the  other  animals  we  have  studied,  that  is,  the 
nephridia.     The  insects  have  lost  the  nephridia. 

/)  The  nervous  system:  Cut  through  the  esophagus,  leaving  it  in  place,  and 
remove  the  digestive  tract.  Look  in  the  median  ventral  line  of  the  abdomen  for 
the  ventral  nerve  cord.  How  many  ganglia  are  present  in  the  abdomen?  Trace 
the  nerve  cord  forward  into  the  thorax.  Note  here,  as  in  the  lobster,  a  so-called 
endoskeleton,  really  an  ingrowth  of  the  exoskeleton,  extending  like  beams  across 
the  floor  of  the  thorax.  Remove  these  and  muscles,  etc.,  so  as  to  expose  the 
thoracic  nerve  cord.  Find  the  three  large  thoracic  ganglia,  one  in  each  segment 
of  the  thorax.  Anterior  to  these  is  the  sub-esophageal  ganglion.  From  this  the 


124  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

circum-esophageal  commissures  pass  forward  around  the  esophagus,  and  unite  at 
the  brain,  or  supra-esophageal  ganglion,  located  between  the  eyes.  Does  the 
nervous  system  of  the  grasshopper  resemble  that  of  the  lobster? 

Draw  in  the  nervous  system  on  your  lateral  view  of  the  grasshopper. 

g)  The  sense  organs:  The  chief  sense  organs  have  already  been  noted.  The 
following  additional  statements  may  be  made.  Read  also  Hegner  (pp.  245-48). 
Insects  are  provided  with  a  great  variety  and  abundance  of  sense  organs.  Much 
work  still  remains  to  be  done  upon  the  structure  and  functions  of  these.  Organs 
of  touch  in  the  form  of  tactile  hairs  are  present  all  over  the  body,  but  particularly 
on  the  antennae,  mouth  parts,  and  cerci.  Organs  of  taste  are  present  as  sensory 
pits  on  the  epipharynx,  hypopharynx,  and  probably  on  the  maxillary  and  labial 
palps.  The  sense  of  smell  is  incredibly  keen  in  insects,  and  is  located  mainly 
upon  the  antennae  in  the  form  of  sensory  pits;  it  is  probable  that  olfactory- 
organs  are  present  elsewhere  also.  Hearing  is  localized  in  the  grasshopper  in 
the  chordo tonal  organ;  in  other  insects  hearing  may  be  served  by  auditory 
hairs  and  auditory  pits.  The  compound  and  simple  eyes  are  the  organs  of  vision ; 
there  is  no  doubt  that  insects  see  objects,  and  they  may  even  perceive  colors, 
but  they  are  especially  quick  in  detecting  movements  of  external  objects,  a 
capacity  undoubtedly  due  to  the  compound  structure  of  the  eyes. 

3.  General  considerations  on  the  grasshopper. — What  are  the  chief  differ- 
ences between  the  external  anatomy  of  the  grasshopper  and  the  lobster?  What 
internal  systems  of  the  two  animals  show  the  most  differences?  What  systems 
of  the  grasshopper  are  -  segmented?  What  particularly  effective  and  highly 
specialized  systems  does  the  grasshopper  possess?  From  your  study  of  the 
anatomy  of  the  grasshopper,  can  you  give  reasons  why  insects  are  the  most 
successful  and  dominant  animals  on  the  earth,  excepting  man? 


C.   GENERAL  SURVEY  OF  ARTHROPODS 

Examine  the  specimens  and  compare  them  with  each  other  and  the  lobster 
and  grasshopper  as  to  degree  of  segmentation,  specialization  and  number  of 
appendages,  general  form,  symmetry,  and  divisions  of  the  body.  The  common 
groups  of  arthropods  are: 

i.  Crustacea,  forms  with  two  pairs  of  antennae,  many  pairs  of  appendages, 
hard  crustaceous  exoskeleton,  and  gills  as  respiratory  organs.  Examine  the 
following  representatives  (not  arranged  by  classification). 

a)  Entomostraca,  small  to  microscopic  Crustacea,  common  in  fresh  water, 
often  inclosed  in  a  bivalve  carapace.    Preserved  forms  are  of  little  value;  living 
forms  if  available  will  be  demonstrated. 

b)  Barnacles,  sessile  forms,  inclosed  in  calcareous  plates.     Marine  forms, 
covering  the  rocks  along  the  seashores. 


PHYLUM  ARTHROPODA  125 

c)  Shrimps,  marine  animals  similar  to  crayfishes,  but  with  a  more  slender, 
delicate  build. 

d)  Crabs,  marine  animals  like  the  lobster,  but  with  a  much  broadened 
cephalothorax,  and  reduced  abdomen  folded  under  the  cephalothorax. 

e)  Amphipods,  small  fresh- water  animals,  something  like  miniature  cray- 
fishes, but  strongly  compressed  from  side  to  side. 

/)  Sow  bugs  or  pill  bugs,  small  forms,  greatly  compressed  dorsoventrally, 
common  in  damp  places,  greenhouses,  etc.,  also  in  water;  curling  into  balls 
when  disturbed. 

2.  Arachnids,  forms  without  antennae,  and  four  pairs  of  walking  legs. 

a)  Spiders,  require  no  description. 

b)  Scorpions,  with  segmented  abdomens  narrowing  to  a  long  tail,  bearing  a 
terminal  sting. 

c)  Daddy  longlegs,  or  harvestmen,  with  small  bodies,  indistinctly  segmented, 
and  very  long  slender  legs. 

d)  Mites,  small,  flattened  forms,  having  lost  all  traces  of  segmentation, 
generally  external  parasites. 

3.  The  king  crab,  or  horseshoe  crab,  survivor  of  an  ancient,  mostly  extinct, 
group,  with  a  large  rounded  cephalothorax;    abdomen  terminated  by  a  long 
sharp  spine. 

4.  Insects,  with  one  pair  of  antennae,  three  pairs  of  walking  legs,  breathing 
by  means  of  tracheae. 

5.  Millipedes  and  centipedes,  elongated  forms  consisting  of  many  segments. 
Each  segment  has  one  pair  of  legs  in  the  centipedes,  and  two  pairs  in  the  milli- 
pedes. 


XIV     FINAL  EXERCISES  ON  COMPARATIVE  ANATOMY 

A.      COMPARISON  OF   CROSS-SECTIONS 

Make  diagrammatic  cross-sections  through  Hydra,  Planaria,  earthworm, 
and  frog,  putting  in  all  the  layers  of  the  body.  Color  ectoderm  blue,  mesoderm 
red,  entoderm  yellow,  peritoneum  and  mesenteries  green.  Indicate  epithelial 
layers  by  crosslines  at  right  angles  to  the  surface;  connective  tissue  by  solid 
shading,  muscles  by  diagonal  lines,  skeleton  by  dots.  After  finishing  these 
diagrams,  study  them  and  be  sure  that  you  understand  thoroughly  what  layers 
correspond  in  the  four  animals,  and  in  what  important  ways  the  sections  differ 
from  each  other. 

B.      COMPARISON  OF  FUNCTIONAL  SYSTEMS 

Make  a  table  as  follows.  Rule  off  a  page  with  vertical  and  horizontal  lines 
so  as  to  make  a  number  of  vertical  and  horizontal  columns.  At  the  left,  in  the 
spaces  between  the  horizontal  lines,  write  the  names  of  all  the  animals  studied 
in  this  course,  beginning  with  the  amoeba  and  ending  with  the  frog,  in  their 
proper  phylogenetic  order.  At  the  tops  of  the  vertical  columns,  going  from 
left  to  right,  write  the  names  of  the  systems  in  the  following  order:  digestive 
system,  muscular  system,  nervous  system,  reproductive  system,  excretory 
system,  circulatory  system,  respiratory  system,  skeletal  system.  In  the  ap- 
propriate spaces  opposite  the  names  of  the  animals,  write  in  very  briefly 
whether  the  animal  has  such  a  system  and  if  so  what  it  consists  of.  The 
table  when  finished  will  illustrate  the  gradual  increase  in  numbers  of  systems 
and  complexity  of  each  system  through  the  animal  kingdom.  Note  that  a 
system  consists  of  parts  set  aside  for  the  performance  of  specific  functions. 
Thus  the  amoeba  respires  but  it  has  no  respiratory  system,  that  is,  no  structure? 
for  that  purpose. 


196 


XV.     EXERCISE  ON  CLASSIFICATION 

The  science  of  classification  or  taxonomy  is  that  branch  of  biology  which 
attempts  to  discover  the  natural  relationships  of  organisms,  and  to  put  all  known 
forms  of  life  in  their  proper  places  in  a  genealogical  tree.  Classification  is  based 
entirely  upon  anatomy,  both  adult  and  embryonic,  and  is  not  in  the  least  con- 
cerned with  function. 

Classification  starts  with  the  conception  of  the  Species,  which  may  be  defined 
for  our  purpose  as  a  group  of  organisms  essentially  alike  in  all  the  details  of  their 
structure.  Thus  all  of  the  frogs  given  out  in  the  laboratory  are  so  nearly  alike 
that  the  laboratory  instructions  even  down  to  the  microscopic  structure  apply 
to  all  individuals.  Such  frogs  therefore  constitute  a  species  and  are  given  a 
name,  called  the  specific  name,  which  is  in  this  case  pipiens.  There  are  many 
other  kinds  of  frogs  which  are  quite  similar  to  this  one  but  differ  in  small  details ; 
for  instance,  the  bullfrog  is  larger,  has  a  different  color  pattern,  and  lacks  the 
dermal  plicae;  it  therefore  receives  another  specific  name,  catesbiana  (see  Holmes, 
pp.  18-21).  There  are  in  fact  about  one  hundred  and  forty  different  kinds  of 
frogs,  each  of  which  has  a  specific  name.  In  order  to  express  the  fact  that  all  of 
these  frogs  are  very  similar  to  each  other  they  are  placed  together  into  one  group, 
called  a  genus.  This  genus  to  which  the  frogs  belong  is  called  Rana,  from  the 
Latin  word  meaning  "frog,"  and  this  name  is  spoken  of  as  the  generic  name.  The 
full  name  of  our  common  frog  is  therefore  Rana  pipiens.  This  system  of  naming 
animals  with  two  names  is  called  the  binomial  system  of  nomenclature  and  was 
devised  by  Linnaeus,  one  of  the  early  biologists  who  became  interested  in  classi- 
fication (see  Hegner,  p.  270). 

Among  the  members  of  a  species  there  are  often  minor  variations,  which  are 
distinguished  as  varieties,  when  sufficiently  important  and  common.  Varieties 
occur  most  frequently  in  domestic  animals.  See,  for  instance,  Hegner's  Fig.  160 
(p.  294)  for  a  photograph  of  the  varieties  of  the  domestic  pigeon. 

All  of  those  genera  which  are  naturally  related  to  each  other  as  shown  by 
their  structure  are  united  together  into  a  family.  Thus  the  lions,  tigers,  leopards, 
lynxes,  and  other  catlike  animals  form  a  natural  family,  the  Felidae,  or  cats, 
having  sharp  fangs,  and  retractile  claws.  Similarly  the  dogs,  wolves,  foxes,  etc., 
form  another  natural  family,  the  Canidae,  in  which  the  claws  are  not  retractile; 
the  bears  are  another  family;  so  also  the  hyenas,  and  the  otters,  weasels,  and 
martens.  All  of  these  families,  together  with  many  others  which  have  not  been 
mentioned,  have  certain  characters  in  common,  such  as  that  they  all  are  carnivo- 
rous and  have  strong  fangs  and  sharp  cutting  teeth,  that  they  have  claws,  and 

127 


128  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

walk  upon  their  tiptoes,  so  to  speak,  and  that  their  skeletons  are  very  similar. 
In  recognition  of  these  facts,  which  demonstrate  that  they  are  related  to  each 
other,  they  are  united  into  a  larger  group,  called  an  order,  in  this  case,  the  order 
Carnivora.  If  we  consider  other  animals  familiar  to  us  we  find  that  they  too 
fall  into  natural  orders;  thus  the  cattle,  sheep,  deer,  horses,  resemble  each  other 
in  that  they  walk  on  their  toenails,  which  are  broadened  into  hoofs,  their  legs 
are  much  modified  for  running,  and  their  teeth  are  broad  and  ridged  for  grinding 
up  vegetable  food.  They  constitute  another  order,  the  Ungulata.  Similarly 
the  rabbits,  squirrels,  mice,  rats,  beavers  constitute  the  order  Rodentia,  dis- 
tinguished by  sharp,  chisel-like  front  teeth. 

If  we  further  consider  these  and  other  orders  of  familiar  quadruped  animals 
we  find  that  they  have  certain  large  characters  in  common,  such  as  that  they  are 
all  clothed  with  fur,  that  their  young  are  born  alive  and  nourished  with  milk, 
and  that  their  skeletons  are  quite  similar.  These  facts  point  to  undoubted 
relationships  between  them,  so  that  they  are  united  into  a  still  larger  taxonomic 
group,  the  class,  in  this  case  the  class  Mammalia,  or  the  mammals. 

The  birds  are  another  natural  class,  distinguished  by  their  covering  of  feathers, 
modification  of  the  fore  limbs  into  wings,  and  egg-laying  habit.  Frogs,  toads,  and 
salamanders  are  another,  with  slimy  smooth  skins;  snakes,  lizards,  alligators 
and  similar  animals  form  another  class,  with  dry  scaly  skins;  fishes  constitute 
a  class  distinguished  by  the  presence  of  gills  and  fins. 

All  of  these  apparently  diverse  classes  of  animals  have  further  certain  common 
characters,  such  as  the  presence  of  an  internal  cartilaginous  or  bony  skeleton, 
consisting  of  skull,  vertebral  column,  limb  girdles,  etc.,  two  pairs  of  appendages, 
a  ventral  chambered  heart,  a  dorsal  nervous  system,  etc.  They  therefore 
together  constitute  one  of  the  great  divisions  of  the  animal  kingdom,  a  phylum. 

The  taxonomic  divisions  are  therefore  variety,  species,  genus,  family,  order, 
class,  phylum.  There  are  usually  other  subdivisions,  also,  as  subphylum,  sub- 
class, suborder,  superfamily,  subfamily,  etc.  Naturally,  the  details  of  classi- 
fication are  not  yet  agreed  upon  because  we  know  as  yet  little  about  the  natural 
relationships  of  animals  and  because  it  is  difficult  to  decide  whether  certain 
characters  are  as  important  as  others,  as,  for  example,  whether  certain  differ- 
ences between  two  animals  will  place  them  in  different  genera  only,  or  whether 
they  are  great  enough  to  separate  them  into  two  different  families.  For  this 
reason  the  student  need  not  be  surprised  to  find  that  the  various  textbooks  do 
not  agree  on  the  details  of  classification,  although  all  recognize  the  same  large 
groups. 

There  follows  a  key  to  the  phyla  and  classes  of  the  animal  kingdom.  Peculiar, 
rare,  and  aberrant  forms  are  not  provided  for  in  the  key,  but  an  attempt  has 
been  made  to  include  all  animals  commonly  met  with.  With  the  aid  of  the  key, 
classify  ten  different  animals  provided  by  the  assistant.  In  this  key  each  state- 
ment of  characters  bears  a  number  followed  in  parentheses  by  one  or  more 


EXERCISE  ON  CLASSIFICATION  129 

numbers  which  refer  to  the  alternative  statement.  If,  therefore,  upon  reading 
the  first  statement  the  student  decides  that  this  does  not  fit  the  animal  in  ques- 
tion, he  turns  at  once  to  the  number  or  numbers  in  parentheses  and  continues 
to  do  this  until  he  finds  a  statement  that  does  fit.  In  this  case  he  proceeds  to 
the  number  given  at  the  end  of  the  statement.  This  method  of  making  a  key 
is  taken  from  Ward  and  Whipple's  Fresh-Water  Biology.  The  key  is  in  part 
derived  from  one  devised  by  Dr.  V.  E.  Shelford,  of  the  University  of  Illinois. 
Only  the  simplest  possible  characters  have  been  chosen  as  means  of  identifica- 
tion, even  though  this  often  involves  repetition  and  increased  length  of  the  key. 

Key  to  the  Phyla  of  Animals 

1  (2).    Animals  consisting  of  a  single  cell,  or  of  a  colony  of  like  cells,  or  masses 
of  multinucleate  protoplasm;  mostly  microscopic.  Phylum  Protozoa 

2  (i).    Animals  consisting  of  many  cells,  of  several  or  many  different  kinds, 
arranged  in  definite  layers.  3 

3  (4,  n).    Without  definite  symmetry.     Forming  sessile  motionless  crusts 
or  masses,  often  branching;  body  porous,  rough,  and  bristly,  pierced  by  numer- 
ous holes,  of  which  one  or  more  are  large  and  conspicuous.      Phylum  Porifera 

4  (3,  n).    With  definite  radial  symmetry.  5 

5  (10).    Relatively   simple   animals,   without   anus,    coelome,   or   definite 
organs.  6 

6  (7).    Sessile,  vase-shaped,  or  cylindrical  forms,  porous,  rough,  bristly,  with 
one  large  terminal,  non-closable  opening;  without  tentacles.    A  few  members 
of  the  Phylum  Porifera 

7  (6).     Soft,  often  gelatinous  animals,  not  porous  or  bristly;  apical  opening 
a  closable  mouth;   nearly  always  with  tentacles.     Parts  of  the  body  arranged 
in  fours  or  sixes  or  indefinite.  8 

8  (9).    With  eight  radial  rows  of  ciliated  swimming  plates;    tentacles,  if 
present,  without  nematocysts.  Phylum  Ctenophora 

9  (8).    Without  such  rows  of  ciliated  plates;    with  tentacles  armed  with 
nematocysts;  often  sessile  and  colonial,  some  free-swimming. 

Phylum  Coelenterata 

10  (5).    More  complex  animals,  with  anus,  coelome,  and  definite  organs; 
parts  of  the  body  almost  always  in  fives,  sometimes  indefinite;  hard,  spiny,  or 
leathery  animals;   tentacles,  if  present,  branched,  and  never  with  nematocysts. 

Phylum  Echinodermata 

11  (4,  3).    With  definite  bilateral  symmetry,  at  least  in  part  of  the  body; 
sometimes  spirally  coiled  in  part;    sometimes  posterior  end  bent  anteriorly 
toward  mouth.  12 

12  (34,  37).     Without  an  internal  cartilaginous  or  bony  skeleton  in  the  form 
of  skull  or  vertebral  column,  wall  of  the  pharynx  not  pierced  with  gill  slits.        13 


130  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGV 

13  (14).     With  one  or  more  girdles  or  crowns  of  cilia  borne  upon  the  discoidai, 
platelike,  or  lobed  anterior  end;  with  internal  movable  chitinous  jaws;  small  or 
microscopic  aquatic  forms.  Phylum  Trochelminthes 

14  (13).     Without  such  crowns  of  cilia.  15 

15  (27).     Body  not  divided  into  segments,  nor  with  segmen tally  arranged 
bristles,  nor  with  segmented  appendages.  16 

1 6  (17,  20).     Wormlike  animals  without  an  anus;  flattened  dorsoventrally, 
often  leaflike  or  ribbon-like;    free-living  in  water,  or  parasitic. 

Phylum  Platyhelminthes 

17(16,20).     Wormlike  animals  with  an  anus;  without  an  exoskeleton;  heads 
poorly  developed  and  not  distinct  from  body.  18 

1 8  (19).     With  a  long  proboscis  inclosed  in  a  sheath  lying  dorsal  to  the 
alimentary  canal,  capable  of  protrusion  from  the  anterior  end;    slender,  often 
very  long,  flattened  to  cylindrical  worms,  mostly  marine.     Phylum  Nemertinea 

19  (18).     Without  such  a  proboscis;    slender  cylindrical  worms,  pointed  at 
each  end,  covered  by  a  smooth  thick  cuticle;  water,  damp  earth,  or  parasitic. 

Phylum  Nemathelmmthes 

20  (17,  16).     Generally  not  wormlike,  with  an  anus;    often  provided  with 
an  exoskeleton,  consisting  of  calcareous  shells  of  one  or  more  pieces,  or  cal- 
careous or  horny  cases  or  tubes,  or  a  gelatinous  secretion;  if  naked,  with  much 
more  definite  heads  than  under  16  and  17.  21 

21  (22).     Colonial  animals,  sessile,  fastened  in  cases,  tubes,  or  on  the  surface 
of  gelatinous  masses;    provided  with  a  circular  or  horseshoeshaped  crown  of 
ciliated  tentacles;  small,  usually  microscopic. 

Phylum  Molluscoidea;  Class  Bryozoa  (Polyzoa) 

22  (21).    Not  colonial,  nor  microscopic,  exoskeleton  in  the  form  of  a  cal- 
careous shell  of  one  or  more  pieces,  or  absent.  23 

23  (24).    With   definite  heads,    sometimes   bearing   tentacles   armed   with 
suckers;  shell,  if  present,  not  bivalve.  Phylum  Mollusca 

24  (23.)     Without  definite  heads;  shell  bivalve.  25 

25  (26).    Halves  of  the  shell  dorsal  and  ventral  in  position;   nearly  always 
fastened  by  a  stalk  protruding  between  the  valves  at  their  hinge. 

Phylum  Molluscoidea;  Class  Brachiopoda 

26  (25).    Halves  of  the  shell  lateral;    never  with  such  a  stalk,  although 
sometimes  sessile.  Phylum  Mollusca 

27  (15).     Body  divided  into  segments,  or  with  segmen  tally  arranged  bristles 
or  internal  organs,  or  with  segmented  appendages.  28 

28  (33).     Without  jointed  appendages;  wormlike.  29 

29  (30).     Remarkably  elongated,  flat,  tapelike  worms,  without  mouth,  anus, 
or  digestive  tract;    head  and  anterior  segments  very  small;    segments  very 
numerous,  increasing  greatly  in  size  posteriorly,  where  they  drop  off  when  ripe; 
always  internal  parasites.  Phylum  Platyhelminthes 


EXERCISE  ON  CLASSIFICATION  131 

30  (20).     Not  tapelike;    with  anus,  mouth,  and  digestive  tract;    segments 
decreasing  in  size  posteriorly  or  of  the  same  size  throughout.  31 

31  (32).     Segments  numerous,  usually  decreasing  in  size  posteriorly;  without 
tracheae,  tracheal  gills,  or  spiracles ;  never  with  definitely  differentiated  chitinized 
heads;   often  with  segmental  bristles,  but  these  never  in  large  tufts  at  one  end 
of  the  body.  Phylum  Annelida 

32  (31).     Segments  few  in  number,  not  exceeding  eleven  or  twelve;    not 
markedly  decreasing  in  size  posteriorly;   with  tracheal  tubes,  tracheal  gills,  or 
spiracles;  often  separate  hard  chitinized  heads;  and  may  have  bristles  in  tufts 
at  one  end.  Phylum  Arthropoda  (insect  larvae) 

33  (28).    With  jointed  appendages,  at  least  on  the  anterior  segments  of  the 
body.  Phylum  Arthropoda 

34  (12,  37).    Wall  of  the  pharynx  pierced  with  gill  slits;  without  an  internal 
cartilaginous  or  bony  skeleton.  35 

35  (36).     Small,  fishlike  forms;  sides  of  the  body  marked  with  zigzag  muscle 
segments;   mouth  without  jaws,  in  the  center  of  a  rounded  hood. 

Phylum  Chordata;  Subphylum  Cephalochorda 

36  (35).    Inclosed  in  a  saclike  gelatinous  or  tough  coat,  which  has  two 
openings  to  the  outside,  for  the  ingress  and  egress  of  water;  sessile,  solitary  or 
colonial  (the  latter  quite  small),  or  free-floating,  marine. 

Phylum  Chordata;  Subphylum  Tunicata 
37.    With  a  cartilaginous  or  bony  skull  and  vertebral  column. 

Phylum  Chordata;  Subphylum  Vertebrata 


Key  to  the  Classes  of  the  Principal  Phyla 
I.    Phylum  Protozoa 

1  (9).    With  temporary  or  permanent  extensions  of  the  surface  of  the  body, 
mostly  for  locomotor  purposes.  2 

2  (3,  6).     Extensions  in  the  form  of  changing  pseudopodia,  blunt  to  long 
and  threadlike.  Class  Sarcodina  (Rhizopoda) 

3  (2,  6).     Extensions  as  raylike,  non-motile  (or  nearly  so)  projections.          4 

4  (5).  Rays  with  a  terminal  knob.  Class  Suctoria 

5  (4).     Rays  pointed,  without  a  knob.  Class  Sarcodina 

6  (2,  3).    Extensions  in  the  form  of  long  or  short,  hairlike,  very  active  pro- 
cesses. 7 

7  (8).    Hairlike  processes  short  and  numerous  (cilia).  Class  Ciliata 

8  (7).    Hairlike  processes  long  and  few  (one  or  two  to  several). 

Class  Flagellata 

9  (i).    Without  locomotor  or  other  processes  of  the  body  in  the  adult  state; 
parasitic.  Class  Sporozoa 


132  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

n.    Phylum  Coelenterata 

1  (4,  7).    Animals  of  the  hydroid  type;  sessile.  2 

2  (3).    Nearly  always  colonial;   body  of  the  hydroids  on  the  end  of  slender 
stalks;  without  an  esophagus,  and  gastrovascular  cavity,  a  simple  sac,  not  divided 
by  septa.  Class  Hydrozoa 

3  (2).     Solitary  or  colonial;   cylindrical  or  columnar,  not  divided  into  body 
and  stalk;    with  an  esophagus,  and  gastrovascular  cavity  divided  into  com- 
partments by  partitions.  Class  Anthozoa 

4  (i,  7).    Animals  of  the  medusa  type,  solitary,  free-swimming.  5 

5  (6).    With  a  velum  and  of  simple  structure.  Class  Hydrozoa 

6  (5).    Without  a  velum,  and  more  complex  in  structure,  usually  with 
highly  branching  gastrovascular  canals.  Class  Scyphozoa 

7  (i,  4).     Complex  floating  colonies  containing  both  hydroid  and  medusa 
types  of  individuals.  Class  Hydrozoa;  Order  Siphonophora 

ffl.    Phylum  Platyhelminthes 

1  (4).    With  mouth  and  digestive  tract;    not  especially  elongated,  nor 
divided  into  segments.  2 

2  (3).    Free-living,  ciliated  forms,  without  suckers.  Class  Turbellaria 

3  (2).    Parasitic,  not  ciliated;   with  at  least  one  sucker,  often  more,  often 
hooks  in  addition.  Class  Trematoda 

4  (i).    Without  mouth  or  digestive  tract;    nearly  always  very  long  and 
tapelike,  and  divided  into  segments  (not  true  segments) ;  parasites. 

Class  Cestoda 

IV.    Phylum  Annelida 

1  (4).    Segmental   bristles  present;    indefinite  number  of   segments;    no 
suckers.  Class  Chaetopoda    2 

2  (3).    Bristles  numerous,  generally  on  lateral  outgrowths,  the  parapodia. 

Subclass  Polychaeta 

3  (2).    Bristles  few,  set  directly  into  the  body  wall;  no  parapodia. 

Subclass  Oligochaeta 

4  (i).    Segmental  bristles  absent;    limited  number  of  segments;    with  an 
anal  and  an  oral  sucker.  Class  Hirudinea 

V.    Phylum  Echinodermata 

1  (8).    With  a  well-developed  skeleton  of  calcareous  ossicles  or  plates; 
usually  spiny;  radial;  no  tentacles.  2 

2  (3).     Mostly  sessile,  attached  by  a  stalk  springing  from  the  aboral  surface; 
if  free,  moving  on  the  aboral  surface.  Class  Crinoidea 


EXERCISE  ON  CLASSIFICATION 


133 


3  (2).     Not  sessile,  nor  stalked;  moving  on  the  oral  surface.  4 

4  (7).     Star-shaped,  five  to  many  rays.  5 

5  (6).     Rays  slender,  sharply  marked  off  from  the  disk. 

Class  Ophiuroidea 

6  (5).     Rays  broad,  not  sharply  separated  from  the  disk.       Class  Asteroidea 

7  (4).     Not  star-shaped;  spherical,  oval,  or  flattened  disks;  very  spiny. 

Class  Echinoidea 

8  (i).     Skeleton  rudimentary;  animals  with  leathery  and  tough  body  walls; 
elongated,  even  wormlike,  with  a  tendency  to  bilaterality;    commonly  with 
branched  tenacles  around  the  mouth.  Class  Holothuroidea 

VI.    Phylum  Mollusca 

i  (2).  With  arms  provided  with  cuplike  suckers;  shell  apparently  absent, 
or,  if  present,  spiral  and  divided  into  chambers.  Class  Cephalopoda 

2(1).  Without  such  sucker-bearing  arms;  shell  never  divided  into  chambers, 
sometimes  absent.  3 

3  (4,  5).     Shell  bivalve.  Class  Pelecypoda 

4  (3>  5)'     Shell  of  eight  pieces.  Class  Amphineura 

5  (3,  4).     Shell  univalve  or  absent.  6 

6  (7).     Shell  shaped  like  an  elephant's  tusk.  Class  Scaphopoda 

7  (6).     Shell  generally  spirally  coiled,   sometimes  cap-shaped  or  conical, 
sometimes  absent.  Class  Gasteropoda 

VII.    Phylum  Arthropoda 

1  (2,  5).     With  two  pairs  of  antennae  in  front  of  the  mouth;    generally 
covered  with  a  hard  exoskeleton;    breathing  by  means  of  gills;    usually  with 
numerous  appendages;  aquatic  or  in  damp  places.  Class  Crustacea 

2  (i,  5).     With  one  pair  of  antennae;  breathing  by  means  of  tracheae.        3 

3  (4).     Elongated,  wormlike,  with  one  or  two  pairs  of  jointed  walking  legs 
on  each  segment  of  the  body.  Class  Myriopoda 

4  (3).    With  only  three  pairs  of  jointed  walking  legs  (larval  forms  of  this 
class  are  provided  for  in  the  key  to  phyla).  Class  Insecta 

5  (i,  2).    Without  antennae;    four  pairs  of  walking  legs  (in  some  cases 
appearing  as  six  pairs  through  leglike  condition  of  mouth  parts). 

Class  Arachnida 

VIII.     Subphylum  Vertebrata 

1  (4).     Fishlike  animals,  living  in  water  and  breathing  by  means  of  gills; 
without  lungs  or  limbs.  2 

2  (3).    Without  jaws,  paired  fins.  Class  Cyclostomata 

3  (2).    With  jaws  and  paired  fins.  Class  Pisces 


134  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

4  (i).    Not  fishlike;  always  with  lungs  (sometimes  gills  in  addition);  paired 
appendages  in  the  form  of  limbs  or  absent.  5 

5  (6).    Skin  naked  and  slimy;  never  marine.  Class  Amphibia 

6  (5).    Skin  provided  with  an  exoskeleton  consisting  of  hairs,  scales,  or 
feathers  (if  apparently  absent,  large  marine  forms).  7 

7  (8>  9)^    Exoskeleton  in  the  form  of  scales,  never  with  hair  or  feathers. 

Class  Reptilia 

8  (7,  9).    Exoskeleton  in  the  form  of  feathers  and  scales.  Class  Aves 

9  (7,  8).    Exoskeleton  in  the  form  of  hairs  (sometimes  apparently  absent, 
sometimes  scales  present  also);  nearly  always  nourishing  the  young  with  milk. 

ClaSS  Mammalia 


XVI.     EXERCISE  ON  ECOLOGY 

Ecology  is  that  part  of  biology  which  studies  living  organisms  in  their  natural 
environments.  Its  problems  are:  (i)  to  locate  every  species  of  plant  and  animal 
in  the  place  which  it  naturally  inhabits;  (2)  to  find  out  and  measure  all  of  the 
factors  which  together  make  up  its  surroundings,  as  physical  factors  (light, 
temperature,  moisture),  chemical  (oxygen  content,  carbon  dioxide  content,  salts 
present),  physiographic  and  metereological  (climate,  seasonal  changes,  composi- 
tion of  soil,  etc.),  and  biological  (other  organisms  present);  (3)  to  discover 
what  structures  the  animal  possesses  which  enable  it  to  maintain  itself  success- 
fully in  its  environment  (e.g.,  if  an  animal  living  in  a  swift  stream  had  not  some 
means  of  hanging  to  objects,  it  would  be  swept  away) ;  (4)  to  determine  how  its 
behavior  enables  it  to  continue  to  live  in  the  environment  in  which  it  is  found  and 
how  it  responds  to  the  various  stimuli  present  in  that  environment,  a  field  of 
work  called  animal  behavior;  (5)  to  study  how  environments  change  through 
physiographic  or  other  processes,  and  how  this  effects  the  organisms  inhabitating 
those  environments.  All  of  these  matters  must  be  determined  not  only  for  the 
adult  but  also  for  all  stages  of  the  life-cycle.  The  problems  of  ecology  are  there- 
fore exceedingly  complex  and  difficult  ones. 

The  class  should  be  conducted  if  possible  on  an  excursion  into  the  field,  into 
any  characteristic  habitat,  as  a  pond,  swift  stream,  woods,  etc.  Each  student 
should  carry  a  number  of  Mason  jars  into  the  field  and  bring  back  to  the  labora- 
tory living  animals  upon  which  experiments  can  be  performed  in  the  laboratory. 
The  animals  are  to  be  placed  as  soon  as  possible  into  conditions  imitating  the 
natural  environment.  As  this  is  easiest  in  the  case  of  pond  animals,  the  pond 
environment  will  prove  one  of  the  most  suitable  for  an  exercise  of  this  kind. 
While  in  the  field  the  student  will  note  carefully  the  various  possibilities  for 
animal  habitats  in  each  general  environment,  as  in  a  pond,  bottom  of  the  pond, 
on  vegetation,  free  in  the  water,  under  floating  objects,  etc.,  and  note  which 
animals  live  in  these  various  places. 

As  a  sample  exercise  in  ecology  the  following  experiments  on  the  pond  snail 
are  presented.  The  common  pond  snails  are  Limnaea,  having  a  long  spiral 
shell;  Planorbis,  flat  spiral  shell;  and  Physa,  short  spiral  shell,  with  the  last 
chamber  much  larger  than  any  of  the  others.  The  instructor  should  furnish 
references  for  reading  in  connection  with  this  exercise. 

i.  Natural  environment  of  the  pond  snail. — Where  were  the  animals  found 
in  the  field?  What  were  they  doing?  What  are  they  doing  now  in  the  laboratory 
aquaria  where  they  have  been  kept  since  collected?  What  are  the  factors  of 

135 


136  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

their  environment?  How  does  it  change  in  the  various  seasons  of  the  year? 
During  the  day?  Is  the  top  water  of  a  pond  different  from  the  bottom  as  to 
light,  temperature,  content  of  oxygen,  carbon  dioxide,  etc.?  What  chemical  sub- 
stances do  you  think  are  present  in  pond  water?  Do  the  snails  occur  where 
there  is  vegetation?  How  does  vegetation  change  the  water  chemically?  How 
would  it  affect  the  penetration  of  sunlight  into  the  pond?  What  is  found  on  the 
bottom  of  the  pond  and  what  role  does  vegetation  play  in  its  production? 

2.  Structures  of  the  pond  snail  which  are  related  to  the  environment. — How 
does  the  animal  move  about?     The  broad  flat  surface  on  which  it  crawls  is  the 
ventral  surface  of  the  body  and  is  called  the  foot.     Is  the  movement  of  the  foot 
a  muscular  one  or  not?     Can  you  see  muscular  waves  passing  along  it?     Con- 
sidering the  method  of  locomotion  of  the  pond  snail  where  would  they  occur 
in  a  pond?     Can  they  swim  free  in  the  water?     How  would  they  reach  the  surface 
of  the  water?     Can  the  animal  go  up  and  down  in  the  water,  without  climbing 
on  objects?     If  you  see  it  doing  so  it  is  traveling  on  a  mucus  thread  secreted  by 
the  foot.     Remove  a  pond  snail  and  throw  it  forcibly  back  into  the  water.     Does 
it  sink?    Does  it  let  out  bubbles  of  air?    The  pond  snails  do  in  fact  possess  a 
chamber  filled  with  air.     By  changing  the  amount  of  air  in  this  chamber,  could 
they  rise  and  sink  in  the  water  at  will? 

The  rounded  projection  in  front  of  the  foot  is  the  head.  It  bears  a  pair  of 
tentacles  at  the  bases  of  which  is  a  pair  of  eyes.  Touch  the  tentacles.  What 
do  you  think  is  their  function?  On  a  snail  which  is  crawling  along  the  sides  of 
the  vessel  so  that  you  can  see  the  underside,  observe  that  a  fold  of  the  body,  the 
mantle,  is  fastened  to  the  inside  of  the  shell.  In  the  center  of  the  ventral  side  of 
the  head  is  the  mouth  opening. 

Pick  up  a  snail  out  of  the  water.  How  far  can  it  withdraw  into  the  shell? 
What  is  the  purpose  of  this  reaction?  What  is  therefore  the  advantage  of  the 
shell?  What  disadvantages  does  its  possession  entail?  What  does  a  snail  do 
when  it  is  violently  disturbed?  Is  this  reaction  ample  to  protect  it  from  enemies? 

Observe  the  mud  in  the  bottom  of  the  jars  where  snails  are  kept,  or  else  put 
some  snails  in  a  jar  of  water  with  mud  in  the  bottom.  Note  the  trails  left  by 
the  snails  as  they  crawl.  Stir  up  a  trail  and  observe  that  the  particles  of  dirt 
stick  together.  How  does  the  snail  accomplish  this?  Is  this  of  advantage  in 
crawling  over  soft  mud  or  slippery  surfaces? 

3.  Food  taking. — As  the  animal  crawls  along  on  the  side  of  the  aquarium 
observe  a  wedge-shaped  object  protruding  from  the  mouth  at  regular  intervals. 
It  is  the  radula.     The  radula  is  a  horny  ribbon  covered  with  teeth,  used  by  the 
snail  for  feeding.     It  is  worked  by  a  complicated  muscular  apparatus  back  and 
forth  over  the  end  of  a  hard  radular  cartilage,  like  a  rope  over  a  pulley,  and  thus 
exerts  a  rasping  action  on  the  food,  reducing  it  to  minute  bits  which  are  then 
sucked  into  the  esophagus.     What  does  a  snail  get  by  rasping  the  glass  of  the 
aquarium?     Do  you  see  evidence  that  the  snails  have  been  feeding  on  the  plants 


EXERCISE  ON  ECOLOGY  137 

in  the  aquarium?  What  would  they  get  besides  plant  tissue  by  scraping  the 
surface  of  vegetation?  Scrape  the  surfaces  of  various  aquatic  plants  and  examine 
the  scrapings  with  a  microscope.  What  do  you  see  (-4)?  Would  you  expect 
to  find  snails  in  bodies  of  water  where  vegetation  is  scanty  or  is  composed  of 
harsh,  tough  plants?  This  gives  us  a  clue  as  to  where  to  look  for  pond  snails 
and  as  to  one  of  the  factors  which  limit  their  distribution.  Examine  a  slide  of 
the  radula  and  note  the  teeth  upon  its  surface. 

4.  Respiration. — Watch  the  snails  for  some  time  and  observe  that  they 
eventually  come  to  the  surface  and  assume  a  characteristic  attitude.     (How 
can  a  heavy  animal  like  a  snail  keep  on  the  surface?)     Observe  between  the  head 
and  the  edge  of  the  shell,  which  is  covered  by  the  mantle,  a  small  conical  pro- 
jection.    This  is  the  respiratory  or  pulmonary  sac.    Observe  that  the  tip  of  the 
sac  is  thrust  above  the  surface  film,  and  is  then  opened  to  the  air.    The  animal 
remains  in  this  attitude  a  little  while  taking  air  into  the  sac.     It  then  closes  the 
sac  and  descends.     The  common  pond  snails  therefore  breathe  air,  but  there  are 
some  fresh-water  snails  which  breathe  by  means  of  gills  and  do  not  have  to  come 
to  the  surface.     By  changing  the  amount  of  air  in  the  pulmonary  sac,  snails 
can  rise  and  sink  in  the  water. 

What  stimulus  do  you  suppose  drives  the  snail  to  the  surface  for  air?  What 
factors  would  determine  how  often  it  would  need  to  come  to  the  surface?  Try 
difference  in  rate  of  taking  air  between  snails  kept  at  ordinary  temperatures  and 
those  in  ice  water.  How  does  the  snail  know  in  which  direction  to  go  for  air? 
To  determine  this,  take  a  wide-mouthed  bottle,  put  some  snails  in  it,  fill  it  com- 
pletely with  water,  and  cork  tightly  so  that  no  air  bubbles  are  included.  Turn 
it  upside  down  and  watch  in  which  direction  the  snails  go  to  seek  air.  Does  this 
answer  the  question? 

How  long  will  snails  live  without  access  to  oxygen?  Take  three  bottles  of 
equal  size,  place  an  equal  number  of  snails  in  each  and  some  vegetation  for  food. 
Fill  two  bottles  completely  with  water  and  stopper  tightly.  Place  one  in  the  ice 
box,  leave  the  other  at  room  temperature.  Fill  the  third  bottle  partly  with 
water  and  leave  open  in  the  room.  How  long  do  the  snails  survive  in  the  stop- 
pered bottles?  Does  temperature  make  a  difference?  Why?  How  would  this 
apply  to  the  living  conditions  of  snails  in  winter,  when  the  ponds  are  covered  with 
ice  and  they  cannot  get  to  the  surface? 

5.  Desiccation  experiment. — Take  a  glass  jar,  put  about  an  inch  of  water 
in  it,  and  several  snails.     Let  stand  until  the  water  is  completely  dried  up.    What 
do  the  snails  do?     Can  they  carry  on  activities  in  the  absence  of  water?    Pick 
one  up  and  examine.    What  do  you  find  across  the  mouth  of  the  shell?    Are 
the  snails  dead?    Put  some  water  in  the  jar  and  note  results.    How  does  this 
apply  to  the  possibility  of  ponds  drying  up  in  hot  weather? 

6.  Reaction  to  light.— Prepare  two  jars  exactly  alike,  filled  with  water  and 
containing  several  snails  and  some  vegetation.     Cover  one  of  them  completely 

11 


138  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

with  black  paper,  except  for  a  vertical  slit  one-half  inch  wide  along  one  side  of 
the  jar.  Place  both  jars  side  by  side  in  a  light  place,  with  the  slit  toward  the 
light.  After  twenty-four  hours  remove  paper  and  note  quickly  the  distribution 
of  the  snails  in  both  jars.  The  one  jar  which  is  not  covered  serves  as  a  control, 
that  is,  it  gives  us  the  distribution  of  snails  on  the  basis  of  chance.  If  the  snails 
in  the  other  jar,  which  is  the  experiment,  are  not  so  distributed,  then  we  may 
conclude  that  light,  the  one  factor  which  is  different  in  the  two  cases,  must  be 
responsible  for  the  different  distribution  of  the  snails  in  the  two  jars.  This  is 
the  way  in  which  every  experiment  must  be  conducted  to  be  convincing.  What 
is  the  reaction  of  snails  to  light?  Do  they  go  to  the  bright  light,  i.e.,  are  they 
found  collected  on  the  slit,  or  do  they  remain  in  the  dark,  or  are  they  to  be  found 
in  weak  light?  How  would  this  affect  their  distribution  in  ponds?  The  condi- 
tion which  an  animal  selects  when  put  in  a  gradient  of  a  particular  factor  is 
called  its  optimum.  It  could  similarly  be  determined  which  temperature  is 
optimum  for  the  snails  by  putting  them  in  a  trough  of  water  which  was  warm 
at  one  end  and  very  cold  at  the  other;  and  any  other  factor  can  be  determined 
in  the  same  way. 

7.  Growth  and  composition  of  the  shell. — Observe  the  parallel  lines  upon  the 
shell.    They  are  lines  of  growth.    The  shell  is  secreted  by  the  mantle  at  its 
margin  and  thus  grows  continually  larger.     Do  small  snails  have  as  many  spiral 
turns  as  large  ones?    The  distance  between  successive  lines  of  growth  records 
the  rate  of  growth.    Can  you  find  places  on  the  shell  where  the  lines  of  growth 
are  so  close  together  as  to  make  one  deep  mark  on  the  shell?    How  do  you  explain 
this?    Could  you  determine  hi  this  way  how  old  a  snail  is?     Put  an  empty  shell 
in  hydrochloric  acid  and  observe  what  happens.     What  does  this  indicate  as  to 
the  composition  of  the  shell?    Is  the  shell  entirely  soluble  in  acid?    What  part 
is  insoluble  and  why?    Does  this  explain  why  the  shells  do  not  dissolve  in  the 
water  in  which  the  animal  lives?    Pond  water  often  becomes  acid  through  the 
decay  of  dead  organisms  in  it  and  the  carbonic  acid  gas  produced  by  the  living 
organisms.     Cut  out  small  pieces  of  shell  in  living  snails,  replace  in  the  aquarium 
and  observe  whether  regeneration  occurs. 

8.  Reproduction. — Egg  masses  of  snails  will  be  commonly  found  in  jars 
where  snails  are  kept.    Where  are  they  placed  by  the  snails?    Why  should  the 
snail  not  simply  drop  them  to  the  bottom  of  the  pond  in  which  it  lives?    Observe 
the  process  of  development  by  removing  eggs  from  time  to  time  and  studying 
under  the  microscope.    In  what  condition  are  the  young  snails  when  they  emerge? 
Are  they  completely  formed? 


SUGGESTIONS  FOR  THE  LABORATORY  ASSISTANTS 

1.  Supplies  for  students. — Each  student  should  be  provided  with  a  jar  or 
vessel  having  a  tight  cover  filled  with  4  per  cent  formaldehyde  (40  c.c.  com- 
mercial formaldehyde  plus  960  c.c.  of  water);  one  or  two  watch  glasses;    and 
a  piece  of  filter  paper.     The  jar  should  be  large  enough  to  receive   com- 
fortably the  animals  used  in  the  course.     The  student  should  keep  these 
materials  in  his  locker  or  elsewhere.     Each  student  will  also  need  a  wax- 
bottomed  dissecting  pan  and  finger  bowls  with  glass  plates  for  covers.    The 
dissecting  pans  are  made  from  low  granite-ware  pans.    The  wax  used  is  cerosin 
(a  commercial  product  obtainable  from  dealers  in  laboratory  supplies),  blackened 
by  lampblack. 

2.  Materials  for  students. — Three  frogs  should  be  allowed  for  each  student. 
The  student  should  be  directed  to  keep  these  frogs  in  the  jar  of  formaldehyde  and 
warned  that  he  will  not  receive  any  others.     One  frog  is  for  the  general  dissec- 
tion; a  second  for  the  work  on  general  physiology;  and  a  third,  injected,  for  the 
circulatory  system  and  nervous  system.     It  is  always  necessary  to  admonish  the 
student  repeatedly  not  to  leave  the  animals  out  on  the  tables  and  not  to  allow 
them  to  become  dry.     Of  the  other  animals  one  specimen  should  be  sufficient. 

3.  Section  on  frog. — Care  should  be  taken  that  the  slit  made  in  the  frog  at 
the  end  of  the  first  laboratory  exercise  is  through  the  skin  only;   if  through 
the  muscles  also  the  viscera  will  protrude  through  the  opening  and  their  rela- 
tions will  be  distorted.     It  is  usually  advisable  to  warn  against  cutting  the  frog 
in  the  median  ventral  line. 

4.  Chemicals  required. — The  following  solutions  and  solids  are  required  in 
the  course;   they  are  required  in  the  order  named: 

a)  Dilute  acetic  acid  for  the  wiping  reflex,  about  10  per  cent,  10  c.c.  of  pure 
glacial  acetic  acid  plus  90  c.c.  distilled  water. 

b)  Powdered  carmine. 

c)  Artificial  gastric  juice:    i  to  2  grams  of  commercial  pepsin,  obtainable 
from  any  drug  house,  in  100  c.c.  of  0.4  per  cent  hydrochloric  acid. 

d)  0.4  per  cent  hydrochloric  acid,  4  c.c.  of  pure  hydrochloric  acid  plus 
996  c.c.  distilled  water. 

e)  Neutral  litmus  solution  can  be  made  by  boiling  litmus  paper,  but  should 
preferably  be  purchased  from  dealers. 

/)  Pancreatic  lipase:  dissolve  one,  to  two  grams  of  commercial  pancreatin, 
obtainable  from  drug  houses,  in  100  c.c.  distilled  water.  Add  enough  sodium 
carbonate  to  render  very  slightly  alkaline. 

139 


140  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

g)  Starch  paste:  stir  up  one  gram  of  starch  (corn  starch  or  any  commercial 
product)  in  a  small  amount  of  cold  water  and  pour  slowly  while  stirring  into 
100  c.c.  of  boiling  distilled  water.  Allow  to  boil  for  a  few  minutes.  Dilute  about 
ten  times  for  using. 

h)  Glucose  solution:  4  or  5  grams  of  glucose  in  a  liter  of  distilled  water. 

i)  Fehling's  solution  consists  of  two  solutions,  not  to  be  mixed  until  ready 
to  be  used.  First  solution,  34.65  grams  of  copper  sulphate  made  up  to  500  c.c. 
with  distilled  water.  Second  solution,  125  grams  of  potassium  hydroxide  and 
173  grams  of  Rochelle  salt  (potassium  sodium  tartrate)  made  up  to  500  c.c. 
with  distilled  water.  Keep  separately  in  rubber-stoppered  bottles.  Just  before 
using  mix  in  equal  quantities,  and  shake  until  the  blue  precipitate  formed  is 
completely  dissolved,  yielding  a  deep  blue,  clear  solution.  The  assistant  should 
mix  the  solutions  just  before  the  laboratory  period  and  give  the  students  the 
mixture. 

j)  Saturated  solution  of  barium  hydroxide;  should  be  clear. 

k)  Physiological  salt  solution:  dissolve  6  to  6j  grams  of  pure  sodium  chloride 
in  a  liter  of  distilled  water. 

/)  Aceto-carmine  stain  (Schneider's):  to  boiling  45  per  cent  glacial  acetic 
acid  (45  c.c.  pure  glacial  acetic  acid  plus  55  c.c.  distilled  water),  add  powdered 
carmine  until  no  more  will  dissolve,  and  filter. 

m)  India  ink  suspension  for  feeding  Paramecium:  get  solid  carbon  sticks, 
obtainable  in  stores  dealing  in  photographic  supplies,  as  it  is  used  for  retouching, 
and  rub  the  stick  in  tap  water  until  a  moderately  black  suspension  is  obtained. 
Do  not  use  ordinary  India  ink  as  this  may  contain  toxic  substances. 

ri)  Picro-acetic  acid:  i  c.c.  of  pure  glacial  acetic  acid,  99  c.c.  of  distilled 
water;  saturate  the  solution  with  picric  acid  crystals. 

0)  Common  salt. 

A  small  bottle  containing  each  of  these  chemicals  should  be  placed  on  each 
table  in  the  laboratory  to  avoid  confusion.  Needless  to  say,  sugar,  starch,  and 
enzyme  solutions  will  not  keep  and  must  be  made  up  fresh  shortly  before  being 
used. 

In  addition  to  the  above  the  assistant  will  require  the  following: 

Ether  or  chloroform. 

Chloral  hydrate  solution  for  macerating  tissues  of  the  frog.  Weigh  out 
5  grams  of  chloral  hydrate  and  add  enough  physiological  salt  solution  to  make 
100  c.c. 

5.  Section  on  general  physiology. — All  of  these  experiments  have  been  tried 
repeatedly  and  have  never  been  known  to  fail.  No  frog  should  be  given  out 
that  is  not  properly  pithed,  as  it  will  certainly  create  a  disturbance.  The 
assistant  should  thoroughly  familiarize  himself  with  the  process  of  pithing.  It 
should  always  be  done  with  a  blunt  instrument,  not  with  a  needle.  Students 
should  be  warned  about  letting  the  frog  dry  up.  Commercial  pepsin  and 


SUGGESTIONS  FOR  THE  LABORATORY  ASSISTANTS  141 

pancreatin  have  always  been  found  reliable.    A  small  percentage  of  human 
beings  have  no  ptyalin  in  their  saliva. 

6.  Section  on  tissues. — This  work  always  proves  rather  difficult,  chiefly 
because  students  use  too  large  pieces.     Verbal  instructions  as  to  the  method  of 
procedure  will  probably  be  more  effective  than  those  written  in  the  outline. 
Shed  epidermis  of  the  frog  will  be  found  in  the  water  in  which  frogs  have  been 
kept  for  a  short  time.     To  prepare  tissues  from  the  intestine,  proceed  as  follows: 
Pith  a  frog.     Cut  out  the  small  intestine,  slit  it  open,  and  wash  it  in  physio- 
logical salt  solution.     For  columnar  epithelium  put  it  into  5  per  cent  chloral 
hydrate  for  twelve  to  eighteen  hours.     For  smooth  muscle,  scrape  off  the  mucosa 
and  place  the  rest,  consisting  of  the  muscular  coats,  in  5  per  cent  chloral  hydrate 
for  twenty-four  to  forty-eight  hours.     Connective  tissue  is  always  best  obtained 
from  a  frog  which  has  been  preserved  in  formalin;  and  striated  muscle  is  usually 
better  from  such  a  source,  unless  the  fresh  muscle  is  carefully  handled.     Fresh 
slices  of  cartilage  are  infinitely  better  than  any  permanent  preparations;  they  are 
obtained  from  the  ends  of  the  long  bones  of  the  frog  with  a  sharp  razor.     Fresh 
blood  may  be  obtained  by  cutting  off  the  toes  of  a  pithed  frog  and  pressing  the 
bleeding  ends  of  the  toes  against  a  slide.     It  is  very  necessary  that  the  physio- 
logical salt  solution  used  for  blood  be  exactly  isotonic  with  the  blood,  or  else  the 
blood  cells  will  become  distorted.     The  myelin  sheaths  of  fresh  nerves  usually 
become  distorted,  producing  appearances  commonly  mistaken  for  nodes  of 
Ranvier.     Students  almost  always  have  trouble  with  the  Golgi  preparations  of 
nerve  cells,  often  mistaking  meaningless  deposits  of  silver  on  the  sections  for 
nerve  cells. 

7.  Section  on  detailed  anatomy. — For  the  study  of  the  circulatory  system, 
injected  frogs  are  essential.     To  inject  a  frog,  etherize  it,  cut  off  the  tip  of  the 
ventricle  and  thrust  the  cannula  of  the  injection  syringe  up  into  the  conus 
arteriosus.     All  of  the  arteries  and  the  postcaval  vein  and  its  branches  are  injected 
in  this  manner.     Veins  are  best  studied  in  freshly  etherized  frogs,  although  they 
are  fairly  satisfactory  in  injected  specimens  if  these  are  injected  shortly  before 
using.     We  have  sometimes  let  the  students  work  out  the  veins  on  freshly 
etherized  frogs  and  then  injected  the  arteries  on  the  same  frogs.     This  has  proved 
satisfactory.    After  the  frogs  are  injected  a  piece  of  the  skull  should  be  removed 
and  the  frogs  placed  in  fairly  strong  formaldehyde,  about  8  per  cent.    This 
serves  not  only  to  harden  the  injected  vessels  but  also  to  harden  the  central 
nervous  system,  which  can  then  be  studied  on  the  same  specimens.     The  injec- 
tion mass  is  made  of  800  c.c.  glycerin,  1,600  c.c.  of  water,  3  boxes  of  cornstarch, 
50  c.c.  of  carbolic  acid  (melted  crystals)  or  thymol,  and  enough  coloring  matter 
of  the  color  desired  (Berlin  blue,  carmine,  chrome  yellow,  etc.)  to  give  a  deep 
brilliant  color  to  the  whole.     Stir  up  before  using.     In  the  case  of  the  frog  it  is 
not  necessary  to  tie  the  cannula  in  the  conus  nor  to  tie  up  the  conus  after  with- 
drawing the  cannula,  but  simply  hold  the  cannula  in  with  the  fingers. 


142  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

8.  Section  on  embryology. — The  frog  material  used  is  preserved  in  formalin. 
Excellent  permanent  mounts  of  halves  of  early  frog  embryos  can  be  made  as 
follows:     Use  slides  provided  with  cells,  or  make  such  a  cell  by  sticking  hard 
rubber  rings  to  the  slide  with  balsam.     Section  the  embryos  with  a  sharp  razor 
and  mount  in  the  cell  in  glycerin  jelly.     The  cover  glass  must  be  sealed  with 
cement  or  varnish.     To  make  glycerin  jelly,  dissolve  6  grams  of  best  gelatin 
in  42  c.c.  of  water,  and  add  50  c.c.  of  glycerin,  and  2  grams  of  carbolic  acid 
crystals.     Warm  (not  above  75°  C.),  and  stir  until  homogeneous.     It  must  be 
liquefied  each  time  used  by  placing  in  warm  water. 

9.  Section  on  Mendel's  law. — Culture  bottles  for  Drosophila  are  prepared  as 
follows:    Use  a  wide-mouthed  eight-ounce  bottle  stoppered  with  cotton.     Put 
a  piece  of  very  ripe  banana  in  the  bottle  and  sterilize.     Stir  up  compressed  yeast 
with  water  to  make  a  paste  and  drop  2  or  3  c.c.  of  this  on  the  banana.     Put  also 
into  the  bottle  a  piece  of  filter  paper  to  absorb  extra  moisture.     The  female 
flies  to  be  used  for  a  breeding  experiment  must  be  isolated  from  males  within 
a  few  hours  after  they  emerge  from  the  pupa  in  order  to  be  certain  that  they  are 
virgin.     Other  directions  for  Drosophila  cultures  are  given  by  Bridges  in  the 
American  Naturalist,  Vol.  LV,  pp.  52-62.     Live  Drosophila  are  sold  by  the  dealers 
mentioned  in  15. 

10.  Section  on  Protozoa. — Cultures  of  Protozoa  and  other  micro-organisms 
may  be  prepared  as  follows: 

a)  Gather  a  lot  of  aquatic  plants,  rotten  lily  pads,  etc.,  from  a  pond,  pack 
into  a  vessel,  add  just  enough  water  to  cover  them,  and  allow  to  decay.     This 
yields  in  about  a  month  very  good  and  lasting  cultures  of  Paramecium,  and 
other  Protozoa. 

b)  Boil  some  wheat  grains  for  a  few  minutes,  and  put  into  jars  of  water  in  the 
proportions  of  about  one  to  two  dozen  grains  to  two  liters  of  water.    Add  a  little 
water,  mud,  or  vegetation  from  a  pond,  or  if  desired  to  raise  a  pure  culture  add 
a  few  individuals  of  the  protozoan  desired. 

c)  Boil  some  hay  in  a  quantity  of  water  for  several  hours  until  the  water 
becomes  dark  brown.     Put  this  brown  water  into  jars  with  a  small  quantity 
of  the  hay  and  inoculate  with  material  from  a  pond  or  withihe  Protozoa  desired. 

These  three  methods  will  yield  all  of  the  common  Protozoa.  Such  cultures, 
when  they  begin  to  die  out,  can  be  rejuvenated  within  two  or  three  days  by 
adding  some  crumbs  of  stale  bread. 

These  methods,  particularly  the  first,  will  commonly  yield  small  amoebae, 
but  it  is  difficult  to  obtain  a  supply  of  large  amoebae  for  a  large  class,  and  they 
had  better  be  purchased  if  possible.  Old  wheat  cultures  which  have  become 
green  often  yield  large  amoebae,  as  do  also  cultures  of  diatoms. 

11.  Section  on  Paramecium. — To   make   Paramecium  stand  still,   gelatin 
solutions,    jelly    made    from    boiled    quince    seed,   and   jelly   from    Chondrus 
(Irish  moss)  have  been  used  satisfactorily  by  many  people,  particularly  the 


SUGGESTIONS  FOR  THE  LABORATORY  ASSISTANTS  143 

last-named  material.  We  have  found  that  a  dilute  solution  of  formalde- 
hyde is  remarkably  effective  for  the  purpose.  Add  one  drop  of  formal- 
dehyde to  100  c.c.  of  water,  and  test  it  on  Paramecium.  If  too  strong 
continue  to  dilute  until  a  strength  is  found  which  seems  to  have  no  effect 
on  the  animals  immediately  but  in  a  few  minutes  causes  them  to  slow 
down  very  gradually.  The  solution  may  be  used  as  directed  in  the  manual 
or  a  drop  of  solution  may  be  placed  alongside  the  edge  of  the  cover  glass.  In 
the  latter  case  a  stronger  solution  will  be  required.  If  the  assistant  will  take 
the  trouble  to  find  out  the  proper  strength  by  trial  in  advance,  he  will  find  the 
method  to  be  very  successful. 

12.  Section  on  Hydra. — To  obtain  Hydra  collect  aquatic  plants,  particularly 
soft  ones,  from  clear  ponds  or  bays  in  sluggish  streams.     Place  the  plants  in 
jars,  using  a  large  amount  of  water  to  a  small  quantity  of  the  plants.    As  the 
animals  become  noticeable,  they  may  be  picked  out  and  placed  in  a  smaller 
vessel.     If  they  are  to  be  kept  for  any  length  of  time  they  must  be  fed  with 
Entomostraca.     To  raise  Entomostraca  place  two  or  three  inches  of  pond  mud 
in  a  glass  vessel,  fill  with  water,  and  throw  in  from  time  to  time  a  few  grains  of 
boiled  wheat.     If  Entomostraca  do  not  appear  of  themselves  in  such  a  culture, 
as  they  usually  will,  a  few  to  start  it  should  be  obtained  from  ponds.     It  is 
possible  by  this  method  to  grow  the  Hydra  and  the  Entomostraca  in  the  same 
vessel,  by  keeping  the  fermentation  of  the  wheat  to  the  lowest  possible  level. 
The  work  with  the  structure  of  the  living  animal  is  always  rather  difficult  for 
students  and  may  profitably  be  omitted.     Small  individuals  are  best  for  the 
purpose. 

13.  Section  on  Planaria. — Planaria  occurs  in  spring-fed  pools  and  in  ponds. 
To  collect  from  springs,  hang  a  piece  of  meat  in  the  current  for  an  hour  or  two, 
whereupon  Planaria,  if  present,  will  attach  to  the  meat  and  may  then  be  shaken 
off  into  a  bottle.     Collect  quantities  of  plants  from  ponds  and  place  in  pans 
with  a  small  quantity  of  water.    After  a  few  days,  as  the  plants  decay,  Planaria, 
if  present,  will  gather  at  the  surface  and  should  be  removed.     Planarians  are 
very  intolerant  of  stagnant  water  and  must  be  kept  in  large  open  pans  in  which 
the  water  is  frequently  changed.     They  should  be  fed  every  few  days  with  fresh 
liver.     The  liver  must  always  be  removed  within  a  few  hours  and  the  pan  and 
worms  thoroughly  washed.     The  digestive  tract  of  Planaria  will  always  stand 
out  plainly  if  the  anaesthetized  animals  are  pressed  out  as  described  in  the 
manual.     However,  it  can  be  made  to  stand  out  beautifully  on  the  intact  animals 
by  feeding  them  on  blood  clots  shortly  before  they  are  to  be  used.     To  demon- 
strate the  feeding  of  Planaria  use  worms  which  have  been  starved  for  a  week 
or  two. 

14.  Section  on  the  earthworm. — The  dissection  of  the  reproductive  system 
should  ordinarily  be  omitted.     Directions  are  given  merely  for  the  sake  of  com- 
pleteness. 


144  LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 

15.  Dealers  in  supplies. — Living  Amoebae  can  be  purchased  from  A.  A. 
Schaeffer,  University  of  Tennessee,  Knoxville,  Tennessee.  Other  Protozoa 
(sometimes  amoeba  also),  Hydra,  Planaria,  etc.,  are  sold  by  Powers  & 
Powers,  Station  A,  Lincoln,  Nebraska.  Various  live  materials,  including  live 
frogs,  preserved  material,  and  prepared  slides  necessary  for  this  course,  are  sold 
by  the  General  Biological  Supply  House,  1177  East  Fifty-fifth  Street,  Chicago; 
the  Anglers  Company,  1534  West  Lake  Street,  Chicago;  and  the  Marine  Bio- 
logical Laboratory,  Supply  Department,  Woods  Hole,  Massachusetts. 


INDEX 


Abdomen:     grasshopper    IIQ,     120; 

lobster  107 
Abdominal  appendages:    grasshopper 

IIQ,  120;   lobster  108 
Abdominal  segment,  lobster  107 
Absorption,  definition  of  18 
Action  of  muscle  56 
Activities.     See  Behavior 
Adrenal  gland  n,  37 
Air  sacs,  grasshopper  121 
Alimentary  canal,  definition  of  9 
Alternation  of  generations  87,  88 
Alternative  inheritance  69 
Alveoli  of  lungs  41 
Amoeba  72-73 

Amoeboid  movement  16,  30,  72 
Amoeboid  organisms  79 
Amphipods  125 
Anaphase  63 
Anemones  88 
Animal  behavior  135 
Animal  hemisphere  66 
Annelida:  in  text  80,  95-132;  in  key 

131, 132 
Antenna:    grasshopper  118;    lobster 

106,  109,  no,  in 
Antennule  106,  107,  109,  no,  in 
Anus:     frog    3,    40;     earthworm  97; 

grasshopper     120,     123;      lobster 

107,  114;    Nereis  96;    Paramecium 
76,  77 

Aortic  arches,  frog  44,  46 

Apex  of  ventricle  9 

Appendages:  biramous  107;  folicae- 
ous  109;  grasshopper  117-20; 
lobster  106-10;  typical  in  lobster 
107;  uniramous  108 

Appendicular:  definition  of  a;  skele- 
ton 51 

Aqueduct  of  Sylvius  48 

Arachnids  125 

Archenteron  66 

Arterial  arches  44 

Arterial  system:  frog  44-45;  lobster 
112,  113,  116 

Arteries:  frog:  carotids  44,  coeliaco- 
mesenteric  45,  common  iliac  45, 
cutaneous  5,  44,  dorsal  aorta  45, 
pulmonary  44,  systemic  arch  44; 
lobster  112,  113,  116 

Artery,  definition  of  9,  20 

Arthropoda:  in  text  81,  106-25; 
in  key  131,  133 

Arthropodial  membranes  107,  117 

Ascaris,  mitosis  in  62-64 

Assimilation,  definition  of  22,  23 

Aster  63 

Asterias,  development  of  65,  66 

Atlas  52 

Auricle  of  heart  9,  45,  46 

Axial,  definition  of  2 

Axial  skeleton  51 

Axis  cylinder  32 

Axone  31,  32 

Barnacles  124 

Basipod,  definition  of  107 

Battery  82,  84 

Behavior:    Amoeba  73;    frog,  15,  19; 

Hydra  83;   Paramecium  74,  76,  77; 

Planaria  go,  92 
Belly  of  muscle  56 
Bilateral  symmetry  2,  61 
Bile  30;  capillaries  33;  duct  39,  40 
Binomial  system  127 
Biramous  appendage  107 
Bladder:    gall  10,  39,  40;    ligaments 

of  8,  zo;  urinary  8,  9,  40,  41 


Blastopore  66,  67 

Blastostyle  87 

Blastula:  frog  66;  starfish  65 

Blood:  cells  of  30,  31;  circulation  of, 
in  earthworm  99;  circulation  of,  in 
frog  20;  composition  of,  in  frog 
20,  30,  31;  corpuscles  of  20,  30,  31; 
function  of  20,  23;  histology  of 
30,31 

Blood  corpuscles:  red  30;  white  30, 31 

Blood  sinuses:  grasshopper  120,  121, 
122;  lobster  112, 113, 115 

Blowfly:  20-23;  adults  20,  21;  egg- 
laying  20;  eggs  21 ;  larvae  21,  22; 
life-cycle  20-23;  pupae  22 

Body  cavity:  earthworm  97,  102; 
frog  6,  7,  8;  origin  in  embryo  67 

Body  wall:  earthworm  97,  98,  101, 
103;  frog  5,  7;  grasshopper  117, 
120, 121 ;  histology  of  in  earthworm 
103;  lobster  in,  112 

Bone,  structure  of  30 

Bones  of  frog  6,  51-55;  kinds  of,  in 
skeleton  51;  hyoid  apparatus  5,  54; 
limbs  55;  lower  jaw  53;  pectoral 
girdle  6,  54;  pelvic  girdle  6,  54; 
skull  52,  53;  sternum  6,  54;  upper 
jaw  53;  vertebral  column  51,  52 

Brachial  plexus  48 

Brachiopoda  in  key  130 

Brain:  earthworm  99,  102;  frog 
12,  46-48;  functions  of  in  frog 
49,  50;  grasshopper  124;  lobster 
115;  Planaria  91 

Branchiae,  lobster  no 

Branchial  chamber,  lobster  107 
108,  no.  in 

Breastbone  6,  54 

Brow  spot  3,  47 

Bryozoa  in  key  130 

Buccal  cavity,  frog  4,  5 

Buccal  pouch,  earthworm  99 

Buds:  Hydra  86;   medusa  87 

Bulbus  arteriosus  9 

Calcareous  body,  frog  48 

Calciferous  glands,  earthworm  99 

Campanularia  86-88 

Capillary  9,  20 

Carapace  106 

Carbohydrates:  definition  of  16; 
digestion  of  18 

Cardiac  chamber,  lobster  114 

Cardiac  end  of  stomach,  frog  39 

Carotid  arch  44;  arteries  44 

Cartilage,  structure  of  29 

Cartilage  bone:  definition  of  51; 
in  skeleton  52 

Cell:  definition  of  24;  body  of 
nerve  cells  31;  division  62-641 
membrane  25;  structure  of  typical 
25,  26 

Cells:  chlorogogue  104;  of  earth- 
worm 103,  104;  of  frog:  blood 
30,  31,  bone  30,  brain  31,  car- 
tilage 29,  connective  tissue  29, 
epithelial  27,  28,  intestine  33,  34, 
kidney  37,  38,  liver  25,  33,  motor, 
of  cord  31,  38,  muscle  28,  29, 
nerve  31,  reproductive  32,  skin 


Cellular  structure  of:  body  wall, 
earthworm  103;  earthworm  103, 
104;  frog  27-38;  Hydra  83-85; 
intestine,  earthworm  104;  intestine. 

145 


frog  33,  34;  kidney  37,  38;  liver 
25, 33J  nerve  cord,  earthworm  114; 
Planaria  92;  skin  36,  37;  spinal 
cord  38;  stomach  35,  36 

Centipedes  125 

Central  canal,  spinal  cord  38 

Centrosome  63,  64 

Centrum  of  vertebra  51 

Cephalization  61 

Cephalothorax  106 

Cerebellum  47,  50 

Cerebral  hemispheres  47,  50 

Cervical  groove  106 

Cestodes  94 

Chaetae  96 

Chaetonotus  80 

Chela  109,  112 

Chitin  106,  117 

Chlorogogue  cells  104 

Choanae  4 

Chordata  in  key  131 

Chordotonal  organ  120 

Chromatin  25,  63,  70 

Chromatophores  16,  20,  36 

Chromosomes  63,  64 

Cilia:  of  cilia te  Protozoa  79;  of 
epithelium  28;  of  flatworms  80; 
of  frog  1 6,  28;  of  Paramecium  75; 
of  Planaria  90;  of  rotifers  80 

Ciliary  movement,  experiment  on  16 

Ciliate  Protozoa  79 

Ciliated  epithelium  28 

Circulation  of  the  blood:  in  earth- 
worm 99;  in  frog  20 

Circulatory  systems:  earthworm  98, 
99;  frog,  general  9;  frog,  special 
41-45;  function  of  20,  23;  grass- 
hopper 121-22;  lobster  112,  113, 
115, 116 

Circum-esophageal     commissures: 
earthworm  102;    grasshopper  124; 
lobster  115 

Cirri  79,  95,  96 

Cisterna  magna  n 

Class,  definition  of  128 

Classification:  definiton  of  127; 
exercise  on  127-34;  of  animals 
120-34 

Cleavage:  of  Asterias  egg  65;  of 
frog  egg  66;  of  starfish  egg  66 

Clitellum  96 

Cloaca  40,  41 

Clypeus  117 

Cnidoblasts  84,  85 

Cnidocil  84,  85 

Coats  of  the  intestine  33-35 

Coelenterata:  in  text  82-89;  in 
key  129,  132 

Coelome:  earthworm  97.  98;  frog 
6-7;  grasshopper  120;  lobster  112; 
origin  in  embryo  67,  71 

Coenosarc  87 

Colony  hydroid  86,  87 

Columella  3,  55 

Conductivity:  definition  of  14; 
experiment  on  14,  15 

Conjugation,  Paramecium  78 

Connective  tissue:  definition  of  29; 
kinds  of  29,  30 

Contractile  vacuole:  Amoeba  72,  73; 
Paramecium  76 

Contractility:  definition  of  15;  ex- 
periment on  15, 16;  of  heart  15, 16; 
of  involuntary  muscle  15;  of 
voluntary  muscle  15 

Conus  arteriosus  9,  44,  45,  46 

Corals  88,  89 

Corium  of  skin  36 


146 


LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 


Cornea  in 

Cornua:     of    gray    matter    58;     of 

hyoid  54 

Corpuscles  20,  30,  31 
Correlation  in  nervous  system  50 
Coxopod,  definition  of  107 
Crabs  125 

Cranial  nerves  12,  47 
Crayfish  106 
Crop:    earthworm   99;    grasshopper 

123 
Cross-section:       comparative      126; 

earthworm  102,  103,  104;   frog  13; 

Hydra  85;  Planaria  92 
Crustacea  124,  125 
Cryptoretic  organs  9 
Ctenophora  in  key  129 
Cultures:   methods  for  Entomostraca 

143;     Hydra    143;     Planaria    143; 

Protozoa  142,  143;   study  of  78-81 
Cuticle:    earthworm  97,  103;   lobster 

106;  Paramecium  75 
Cyclops  51 

Cystic  ducts  of  liver  40 
Cytopharynx  75 
Cytoplasm,  definition  of  25 

Daddy  longlegs  125 

Death,  meaning  of  i 

Defecation,  definition  of  19 

Dendrite  31 

Dermal  bone,  definition  of  51 

Dermis  of  skin  36 

Development:  Asterias  65-66;  blow- 
fly 20-23;  definition  of  20,  65; 
Drosophtla  20-23;  fly  20-23;  frog 
66-68;  general  account  of  71;  star- 
fish 65-66 

Diastase:  definition  of  17;  experi- 
ment on  1 8 

Diencephalon  47,  48,  50 

Digestion:  definition  of  16,  17; 
experiments  on  17,  18 

Digestive  apparatus,  Paramecium 
?6,  77,  78 

Digestive  gland,  lobster  112,  114 

Digestive  system:  earthworm  99, 
100;  frog,  general  9;  frog,  special 
39-40;  functions  of  16;  grasshopper 
123;  Hydra  82;  lobster  114; 
Planaria  91 

Dominant  character  69 

Dorsal  aorta  45 

Drosophila:  breeding  experiment 
69-70;  life  cycle  20-23;  method  of 
culture  142 

Drum  membrane  2 

Duodenum  10,  39 

Ear:  frog  3;  grasshopper  120 
Earthworm  96-104;  circulatory  sys- 
tem 98;  coelome  97;  digestive 
system  99,  100;  excretory  system 
100;  external  anatomy  96-97;  in- 
ternal anatomy  97-102 ;  microscopic 
structure  102-4;  muscles  102,  103; 
nerve  cord  104;  nervous  system 
101,  102;  reproductive  system 

IOO,  IOI 

Echinodermata  in  key  129,  132 
Ecology:  definition  of  135;  exercise  on 

135-38 
Ectoderm:    embryo  66,  67,  71;    fate 

of,  in  frog  67;    general  function  of 

71;   Hydra  83,  85;  Planaria  go,  92 
Ectoplasm  72,  75 
Ectosarc  75 

Egestion,  definition  of  19 
Egg,  development  of  65-68 
Egg  guide  1 20,  122 
Egg-laying  of:    flies  20;    grasshopper 

120,  122,  123 
Eggs:    Ascaris  62-64;    definition  of 

20;    fish  64;    flies  20-21;    frog  32; 

sea-urchin  26;  starfish  65 
Embryology  65-68;    Asterias  65-66; 

frog  66-68;   starfish  65-66 
Endocrinous  organs  8 
Endophragmal  skeleton  115 


Endoplasm:  Amoeba  72;  Paramecium 

Endopod,  definition  of  107 

Endosarc  75 

Endoskeleton:  definition  of  51; 
frog  51-55 

Entoderm:  embryo  66,  67,  71; 
fate  of,  in  frog  67;  general  function 
of  71;  Hydra  83,  85;  Planaria  90 

Entomostraca  81,  124 

Environment,  factors  of  135,  136 

Enzymes:  definition  of  17;  experi- 
ments on  17,  18 

Epicranium  117 

Epidermis:  earthworm  102,  103; 
frog  27,  36;  grasshopper  117; 
lobster  in;  Planaria  92 

Epimeron  107,  117 

Epipharynx  118 

Epithelial  tissues  27-28 

Epithelium:  ciliated  28;  columnar 
27;  definition  of  27;  in  earthworm 
104;  in  Hydra  85;  in  intestine  of 
frog  34;  in  Planaria  92;  squamous 
27;  stratified  36 

Esophagus:  earthworm  99;  frog 
S>  19.  391  grasshopper  123;  lobster 
114 

Eustachian  tube  4 

Excretion,  definition  of  19 

Excretory  systems:  earthworm  100; 
frog,  general  1 1 ;  frog,  special  40, 41 ; 
function  of  19,  23;  grasshopper  123; 
lobster  115;  Planaria  91 

Exopod,  definition  of  107 

Exoskeleton:  definition  of  51;  grass- 
hopper 117;  lobster  106 

Eyelids,  frog  2 

Eyes:  frog  2;  grasshopper  117; 
lobster  106,  in;  Nereis  95;  Plan- 
aria  90,  91;  snail,  136 

Family,  in  classification  127 

Fascia:    definition  of  56;    dorsal  57; 

lata  59 

Fat  body:    frog  n;   grasshopper  121 
Fats:    definition  of  16;    digestion  of 

17,  18 

Feces,  definition  of  19 
Fehling's  solution  18,  140 
Fertilization:     definition   of    20,    65; 

membrane  65 

Fibers  of  connective  tissue  29 
Fish  eggs,  mitosis  in  64 
Fission,  Paramecium  77,  78 
Flagellates  80 
Flagellum,  definition  of  80 
Flatworms  80 


Flukes  93 
Fly:     adu 


Fly:  adult  anatomy  21;  blowfly 
20-23;  eggs  21;  fruit  fly  21; 
larvae  21,  22;  life-cycle  21-23; 
pupae  22 

Foliaceous  appendage  109 

Food  ingestion:  Paramecium  76,  77; 
Planaria  92,  93;  snail  136,  137 

Food  vacuoles:  Amoeba  73;  Para- 
mecium 75,  76,  77 

Foot,  snail  136 

Foramen  magnum  52 

Foramen  of  Monro  48 

Frog  (1-61):  arterial  system  44-45; 
blood  30,  31;  body  wall  5-7; 
brain  46-48;  buccal  cavity  4-5; 
circulation  of  the  blood  20;  circu- 
latory system:  function  20,  general 
anatomy  9,  special  anatomy 
41-46,  coelome  6-7;  cross-section 
13;  digestive  system:  function 
16-18  general  anatomy  9-10, 
special  anatomy  39-40;  excretory 
system:  function  ip,  general 
anatomy  5,  special  anatomy 
40-41;  external  anatomy  1-3; 
glands  of  internal  secretion  7. 
ii,  12;  heart  45,  46;  histology  of 
tissues  24-32;  histology  of  organs: 
intestine  33,  34,  kidney  37,  38. 
liver  33,  skin  36,  37,  spinal  cord 
38,  stomach  35,  36;  internal 


anatomy:  general  5-13,  special 
39-61;  mesenteries:  general  state- 
ment 7.  8,  of  bladder  8,  10,  of 
digestive  tract  10,  of  reproductive 
system  u;  muscles:  abdomen  6, 
58,  function  15-16,  general  5-6, 
hyoid  apparatus  58,  59,  lower  jaw 
57,  58,  parts  of  a  muscle  56,  shank 
60,  61,  thigh  59,  60,  tongue  59; 
nervous  system:  function  14,  49,  50, 
general  anatomy  12,  special  ana- 
tomy 46-49;  physiology:  digestive 
system  16-18,  circulatory  system 
20,  excretory  system  19,  muscular 
system  15-16,  nervous  system 
14-15,  reproductive  system  20-23, 
respiratory  system  18-19,  summary 
23;  reproductive  system:  general 
anatomy  4-5,  special  anatomy  40- 
41;  respiratory  system:  function 
18,  19,  general  anatomy  9,  special 
anatomy  41;  sense  organs  12; 
skeleton:  hyoid  apparatus  5,  54, 
limbs  55,  lower  jaw  53,  pectoral 
girdle  6,  54,  pelvic  girdle  6,  54, 
skull  52,  53,  sternum  6,  54,  upper 
jaw  53,  vertebral  column  51,  52; 
tissues:  blood  30,  31,  connective 
29,  30,  epithelial  27,  28,  muscular 
28,  29,  nervous  31-32,  reproduc- 
tive 32;  urinogenital  system: 
general  anatomy  4,  5,  special 
anatomy  40-41;  venous  system 
41-44 

Frons  117 

Fruit  fly  21-23 

Gall  bladder  10,  39,  40 

Ganglia:  earthworm  101.  102,  103; 
grasshopper  123,  124;  lobster  115, 
116;  spinal  48,  49;  sympathetic  12 

Ganglion,  definition  of  49 

Gastric:  gland,  frog  35;  juice  17; 
mill  114;  muscles,  lobster  in,  114 

Gastrolith  114 

Gastrovascular  cavity:  definition  of 
82;  Hydra  82,  83;  Planaria  91 

Gastrula:  Asterias  66;  frog  66; 
general  significance  71;  starfish  66 

Gastrula  stage,  general  71 

Gena  117 

Generic  name,  definition  of  127 

Genus,  definition  of  127 

Germ  layers  in  embryo  66,  71 

Giant  fibers  104 

Gill:  slits  of  tadpole  68;  supports, 
tadpole  52 

Gills,  lobster  107,  108,  109,  no 

Gizzard:  earthworm  99;  grasshopper 
123 

Glands:  of  frog:  adrenal  n,  37, 
cutaneous  36,  gastric  35,  mucous 
36,  37,  poison  37;  01  internal 
secretion  8,  n 

Glomerulus  38 

Glottis  5,  41 

Goblet  cells  27,  34 

Gonads,  definition  of  10 

Gonotheca  87 

Gonozooids  87 

Grasshopper:  abdomen  ^  119-120; 
appendages  117-20;  circulatory 
system  121-22;  digestive  system 
123;  excretory  system  123;  exter- 
nal anatomy  117-20;  head  117-18; 
internal  anatomy  120-24;  nervous 
system  123-24;  reproductive  120, 
122-23;  respiratory  system  121; 
sense  organs  117,  118,  124;  thoraj 
118-19 

Gray  matter  of  cord  31,  38 

Green  gland  115 

Gullet,  Paramecium  75 

Haversian  canals  30 

Head:  earthworm  96;  frog  1-5; 
grasshopper  117-18;  lobster  106, 
107,109,110;  Nereis  95;  Planaria 
go;  snail  136;  appendages:  grass- 
hopper 117-18,  lobster  109-10. 


INDEX 


147 


Nereis  95;  dominance  of  61;  of  a 
muscle  56 

Heart:  frog  9,  45,  46;  grasshopper 
121,  122;  lobster  112,  113 

Heart  beat  15 

Hearts,  earthworm  98 

Heliozoa  70 

Hepatic:  ducts  40;  portal  system  42; 
portal  vein  42 

Heredity  experiment  69-70 

Histology:  definition  of  24;  earth- 
worm 102-4;  frog,  organs  ,33-38; 
frog  tissues  24-33;  Hydra  83-85; 
intestine,  frog  33,  34;  kidney,  frog 
37,  38;  liver  33;  Planaria  92; 
skin,  frog  36,  37;  spinal  cord, 
frog  38;  stomach,  frog  35,  36 

Horns  of  gray  matter  38 

Horseshoe  crab  125 

Hybrids  69,  70 

Hydra:  behavior  83;  cells  of  83-85; 
cross-section  85;  general  structure 
82;  nematocysts  82,  84;  repro- 
duction 86;  reproductive  organs 
86 

Hydranth  87 

Hydroid  colony  86-88 

Hydrotheca  87 

Hyoid  apparatus  5,  41,  53,  54;  mus- 
cles of  58,  so 

Hypophysis  48 

Hypostome  82 

Ileum  39 

Inferior  lobes  48 

Infundibulum  48 

Insects  125;   in  key  131,  133 

Insertion  of  muscle  56 

Intercellular  substance:  definition  of 
26;  in  blood  30;  in  connective 
tissue  29;  in  epithelium  27;  in 
muscle  28 

Intestine:  earthworm  100,  104; 
frog  o,  10,  39,  40;  grasshopper  123; 
histology  of,  in  earthworm  104; 
histology  of  in  frog  33-35;  lobster 
114;  Planaria  91 

Investing  bone,  definition  of  51 

Iris  2 

Irritability:  definition  of  14;  experi- 
ment on  14,  15;  of  Amoeba  73; 
of  Hydra  83;  of  nervous  system 
14,  15;  of  Paramecium  77;  of 
Planaria  90 

Jaws:  bones  of  frog  52,  S3!  fly  larva 
22;  frog  4-5;  muscles  of  frog 

57-58 
Jellyfish  88 

Karyokinesis  62 

Key:  to  classes  131-34;  to  phyla 
129-31 

Kidney:  frog  n,  37,  40,  41;  func- 
tions of  19,  23;  histology  of  37 

King  crab  125 

Labrum:  grasshopper  117,  118; 
lobster  no 

Lacuna:  bone  30;  cartilage  29 

Ladder  type,  nervous  system  116 

Large  intestine,  frog  9,  40 

Larvae,  fly  21-22 

Laryngeal  chamber  41 

Laryngeal  prominence  5 

Larynx  9,  91 

Leeches  105- 

Legs,  parts  of:  grasshopper  ng; 
lobster  108,  109 

Leucocytes  30 

Life-cycle  fly  20-^23 

Ligament  definition  of  7 

Ligaments  of  frog:  coronary  g,  10; 
falciform  of  liver  8;  hepato-gastro- 
duodenal  10,  39;  lateral  of  bladder 
10;  median  of  bladder  8,  10; 
rectovesical  10;  suspensory  of 
liver  8,  *o.  See  also  under  Mesen- 
teries 


Limbs  of  frog:  bones  of  55;  external 
anatomy  of  3;  muscles  of  59,  60,  61 

Linea  alba  6 

Linin  network  25 

Linnaeus  127 

Lipase:  action  of  17;  definition  of  17; 
experiment  on  17 

Liver:  cells  25;  frog  8,  39;  histology 
of  33;  lobes  of  39;  lobster  114 

Lobes:  of  brain  46,  47;  of  liver  39 

Lobster:  abdomen  106,  107,  108; 
abdominal  appendages  107;  append- 
ages 107-10;  circulatory  system 
112,  113,  115,  116;  digestive  sys- 
tem 114;  excretory  system  115; 
external  anatomy  106-11;  head 
106-7;  head  appendages  100-10; 
internal  anatomy  111-16;  muscles 
111-12;  nervous  system  115-16; 
reproductive  system  113-14;  res- 
piratory system  no-ii;  segmen- 
tation 106-16;  sense  organs  in; 
thoracic  appendages  107-8,  109, 
no,  in;  thorax  106,  107,  no,  in 

Lungs  9,  41 

Lymphocytes  31 

Lymph  5:  sac  subvertebral  n; 
sacs,  frog  5,  n,  13;  spaces,  frog  5, 
ii 

Malpighian  bodies  of  kidney  37; 
tubules  123 

Mandible:  frog  53,  57;  grasshopper 
118;  lobster  109,  no 

Mandibular  arch,  frog:  bones  of  53; 
muscles  of  57 

Matrix:  of  bone  50;  of  cartilage  29; 
of  connective  tissue  29 

Maxilla:  grasshopper  118;  lobster 
109,  1 10 

Maxillary:  arch,  bones  of  53;  teeth 
4,  53 

Maxillipeds  108,  109 

Meckel's  cartilage  53 

Medulla  oblongata  47,  50 

Medullary  folds  67;  sheath  32 

Medusa  buds  87 

Medusae  87,  88 

Membrane  bone  51.  52 

Mendel  70 

Mendel's  law  69,  70 

Mesenteries,  earthworm  97 

Mesenteries,  frog  7,  8,  10,  n;  dorsal 
8,  10;  dorsal  of  liver  10;  mesentery 
of  intestine  10;  meso-esophageum 
10;  mesogaster  10;  mesorchium 
11,  40;  mesorectum  ii;  mesotu- 
barium  11;  mesovarium  n,  4^1; 
ventral  8,  10.  See  also  under  Lig- 
aments 

Mesentery,  definition  of  7 

Mesoderm:      embryo     66,     67,     71; 
fate  of,  in  frog  67;  general 
canceof7i;  Planaria  go,  92 

Mesogloea,  83,  85 

Mesothorax  118,  119 

Metabolism,  definition  of  23 

Metagenesis  87,  88 

Metamere,  definition  of  gs 

Metamorphosis,  definition  of  22 

Metaphase  63 

Metathorax  118,  119 

Millipedes  125 

Mites  125 

Mitosis  62-64 


Mitotic  figure  63 
Mollusca  in  key  130, 


133 


Molluscoidea  in  key  130 
Morphology,  definition  of  14 
Mouth:      cavity:      earthworm     gg, 
frog   44;    earthworm   96,    frog  4; 
grasshopper  1 1 8;  Hydra  82;  lobster 
107,  no;    Nereis  95;    Paramecium 
75;     Planaria    91;      parts:    grass- 
hopper 117,  118;   lobster  107,  109, 
no 

Mucus  (33,  103,  go):  cells:  earth- 
worm 103,  Planaria  go,  92;  glands: 
earthworm  103,  frog  36,  Planaria 
92;  thread  of  snail  136 


Muscle:  cells,  structure  of  28,  2g: 
contractility  of  15;  function  of 
15,  16;  heart  15,  16;  involuntary 
15,  28;  kinds  of  15,  28,  29;  micro- 
scopic structure  of  28,  29;  parts  of 
56;  smooth  28;  striated  28,  29 
typical  56;  voluntary  28,  29 

Muscles  of:  abdomen,  frog  58;  body 
wall  earthworm  102,  103;  body 
wall  frog  5-6;  chela  112;  earth 
worm  102,  103;  frog  5,  6,  15,  56-61; 
grasshopper  121;  Hydra  85;  hyoirl 
apparatus  58;  lobster  in,  112; 
lower  jaw  frog  57,  58;  Planaria  92; 
shank  frog  60;  thigh  frog  59; 
tongue  frog  58,  59;  trunk  frog 


Muscular:  system:  earthworm  102, 
103,  frog  5,  6,  15,  56-61,  function 
of  15;  grasshopper  121,  Hydra  85, 
lobster  in,  112.  Planaria  92; 
tissue,  structure  of  28,  29 

Myelin  32 

Naids  80 

Nares:  external  2;  internal  4; 
method  of  closure  58;  respiratory 
movements  of  18,  19 

Nemathelminthes  80;  in  key  130 

Nematocysts  82,  84,  85 

Nematodes  80 

Nemertinea  in  key  130 

Nephridia:  earthworm  g8,  zoo,  102; 
lobster  115 

Nephridiopore  100 

Nephrostome  100 

Nereis  95,  96 

Nerve:  conductivity  in  14,  15; 
definition  of  31;  irritability  of  14, 
15;  roots  of  51;  sciatic  15;  stim- 
ulation of  15;  structure  of  32 

Nerve  cells:  brain  31;  earthworm 
99,  102,  104;  frog  31,  32  38;  lobster 
i  n ;  motor  of  cord  31,32;  Planaria 
90,  92;  spinal  cord  frog  38;  struc- 
ture of  31,  32 

Nerve  cords:  earthworm  99,  102,  104; 
grasshopper  123,  124;  lobster 
115,  116;  Planaria  92 

Nerve  plexus,  frog  48 

Nerves:  cranial,  frog  12,  47;  roots 
of  51;  spinal,  frog  12,  48,  49 

Nervous  system:  central,  frog  12, 
46-50;  earthworm  101,  102;  frog 
12,  46-50;  function  of  14,  40-50; 
grasshopper  123.  124;  Hydra  86; 
lobster  115,  116;  origin  of,  in 
embryo  67;  peripheral,  frog  12, 
47-49;  Planaria  91,  92;  sympa- 
thetic, frog  12 

Neural:  arches  12,  51;  canal  12,  47, 
51;  fold  67;  spine  51 

Neurilemma  32 

Neuroglia  38 

Nictitating  membrane  4 

Nostrils  2 

Notochord  67 

No  turn  117 

Nuclear  membrane  25 

Nucleolus  26,  64 

Nucleus:  Amoeba  73;  definition  of 
24;  in  mitosis  62-64;  Paramecium 
76;  structure  of  25,  26 

Nutritive  zooids  87 

Obelia  86-88 

Ocelli  117 

Occipital  condyles  53 

Olfactory   lobes   46,    50;     nerve   47; 

sense:    frog  50;    grasshopper  124; 

lobster  in;  Planaria  91,  92 
Ommatidia  in,  117       ' 
One-celled  animals  72-80 
Ontogeny,  definition  of  20 
Optical  section,  definition  of  65 
Optic  chiasma  48;    ganglion,  lobster 

ii  i ;  lobes  47,  50;  nerves,  frog  47 
Oral  groove  74 
Orbit  2,  52 
Order  in  classification  128 


148 


LABORATORY  MANUAL  FOR  ELEMENTARY  ZOOLOGY 


Organ,  definition  of  8 

Origin  of  a  muscle  56 

Ossicles  114 

Ostia    of    heart:     grasshopper    122; 

lobster  113 
Ostium  of  oviduct  41 
Ova:     definition   of   20;    of   fly    21; 

of  frog  10,  32;    of  sea-urchin  26; 

of  starfish  65;   structure  of  26 
Ovaries:    earthworm  101;    frog  9,  10, 

41;     function   of    20;    grasshopper 

122;  Hydra  86;   lobster  114 
Oviducts:    earthworm  101;    frog  n, 

41;    grasshopper  122;    lobster  114; 

male  frog  n,  40;  ostium  of  41 
Ovipositor  120,  122 
Oxidation,  definition  of  19,  23 

Palps:  grasshopper  118;  Nereis  95 

Pancreas  9,  39,  40 

Pancreatic  ducts  40 

Paramecium  73-78;  avoiding  reaction 
77;  behavior  74,  76,  77;  conjuga- 
tion 78;  digestive  apparatus  75,  76; 
experiments  on  76,  77;  fission 
77-78;  food  ingestion  76,  77; 
reaction  to  chemicals  77;  repro- 
duction 77-78;  structure  74-76 

Parapodium  95,  96,  105 

Parenchyma  92 

Pectoral  girdle:  bones  of  6,  54;  defini- 
tion of  6;  muscles  of  58 

Pelvic  girdle:  bones  of  6,  54,  SSI 
definition  of  6;  muscles  of  58, 
50.  60 

Penis  120,  122 

Pepsin  17 

Pereiopods  108,  109 

Pericardial  cavity  7;  sac  7 

Pericardium  7 

Perisarc  87 

Peristalsis,  definition  of  15 

Peristomium  95,  96 

Peritoneum:  definition  of  7;  earth- 
worm 98;  frog  6,  7,  8,  ii ;  origin  of, 
in  embryo  67;  parietal  7,  98; 
visceral  7,  98 

Pharyngeal  chamber  91,  92 

Pharynx:  earthworm  99;  frog  39; 
Nereis  95;  Planaria  91,  92 

Phyla,  key  to  129,  131 

Phylum,  definition  of  72,  128 

Physiology:  definition  of  72;  of 
circulatory  system  20;  of  digestive 
system  16-18;  of  frog  14-23; 
of  excretory  system  19;  of  muscular 
system  15-16;  of  nervous  system 
14,  15,  49-50;  of  reproductive 
system  20-23;  of  respiratory  sys- 
tem 18, 19;  of  skin  19;  summary  23 

Pia  mater  38,  46 

Pigment  cells:  liver  33;  skin  16,  36, 
20;  granules:  liver  33;  PlananaQo 

Pill  bugs  125 

Pineal  body  3,  47 

Pithing,  method  of  i 

Planaria:  behavior  90;  cross-section 
p2;  digestive  system  91;  food 
ingestion  92,  93;  histology  92; 
regeneration  93;  sense  organs  90, 
91 ;  structure  90-92 

Plasma,  definition  of  20,  30 

Plasmosome  26 

Platyhelminthes:  in  key  130,  132; 
in  text  80,  90-94 

Podical  plates  1 20 

Polychaetes  in  key  132;  in  text  105 

Polymorphism  87-88 

Polyp  87 

Pond  snail  135-138.     See  under  Snail 

Porifera  in  key  129 

Portal  system:  definition  of  43; 
hepatic  portal  43;  renal  portal  43 

Prehallux  3 

Proboscis,  Planaria  91 

Pronotum  118,  119 

Prophase  63 

Prostomium  95,  96 

Protease:  action  of  17;  definition  of 
17:  experiment  with  17 


Proteins:   definition  of  16;   digestion 

of  17 

Prothorax  118,  119 
Protoplasm,  definition  of  24 
Protopod,  definition  of  117 
Protozoa:    ciliate   79;    flagellate  80; 

definition  of  72;    m  key  129,  131; 

in  text  71-80 
Pseudopodia  72 
Pseudothyroid  12 
Ptyalin  18 
Pulmonary  artery  44;   sac,  snail  137; 

vein  43 
Pulse  20 
Pupae,  flies  22 
Pupil  12 
Pyloric      chamber     114;      division, 

stomach  39 
Pylorus  39 

Radula  136,  137 

Ramus  communicans  12,  49 

Reaction,  definition  of  14 

Reaction  time:  definition  of  14; 
of  involuntary  muscle  15;  of  nerve 
14,  15;  of  voluntary  muscle  15 

Reactions  of  animals.     See  Behavior 

Recessive  character  69 

Rectum:  frog  40;  grasshopper  123; 
lobster  114 

Reflex:  definition  of  14,  50;  in  frog 
14,  15,  50;  wiping  14,  15 

Regeneration,  Planaria  93 

Renal  portal  system  43 

Reproduction,  method  of:  earth- 
worm 96;  flies  20-23;  grasshopper 
1 20,  122,  123;  Hydra  86;  Parame- 
cium 77,  78;  snail  138 

Reproductive  cells  32;  systems: 
earthworm  100-101,  frog,  general 
10,  frog,  special  40,  41,  function  of 
20-23,  grasshopper  120,  122-23, 
Hydra  86,  lobster  113,  114 

Respiration:  definition  of  18;  external 
18;  frog  19;  function  of  18,  19,  23; 
insect  larvae  21 ;  internal  19;  mus- 
cles of  58,  59;  grasshopper  121; 
snail  137;  through  skin  of  frog  19 

Respiratory  function  of  the  skin  19; 
movements  of  frog  18,  19;  sac  137; 
system:  fly  larvae  21;  fly  pupae  22, 
frog,  general  9,  frog,  special  41, 
function  of  18,19,  grasshopper  121, 
insects  22,  121,  lobster  no,  in 

Response,  definition  of  14 

Resting  cell  62 

Retroperitoneal,  definition  of  11 

Rhabdites  90,  92 

Ribs  6 

Root  cap  plants  64 

Root  tips,  mitosis  in  64 

Roots  of  spinal  nerves  47,  49 

Rostrum  106 

Rotifers:  in  key  130;  in  text  80 

Roundworms:  in  key  130;  in  text  80 

Rugae,  stomach  35,  39 

Sacral  vertebra  52 

Sagittal  axis  2;  plane  a,  61 

Saliva,  action  of  18 

Sarcolemma  28 

Sarcostyles  29 

Sciatic  nerve  15;  plexus  48 

Sclerite  117 

Scorpions  125 

Sea  fans  89;  feathers  89 

Segmentation:  cavity  65;  earthworm, 
coelome  97,  98;  earthworm,  body 
96;  of  the  egg  65-66;  embryo  68; 
fly  21-22;  frog,  adult  61;  frog, 
tadpole  68;  general  discussion  of 
61,  68,  71;  grasshopper  117; 
insects  21,  22,  117;  Nereis  95,  96; 
lobster  106,  116;  tadpole  68 

Segments:  definition  of  21,  61,  68; 
embryo  68;  earthworm  96;  fly 
21-22;  frog  61;  grasshopper 
117-20,  124;  insects  22-22;  lobster 
106,  107-110,  112.  116:  Nereis 
o*  06:  tadpole  68 


Seminal  funnel  101;  receptacles  98, 
100,  101;  vestcles  98,  100,  101 

Sense  centers,  brain  49,  50 

Sense  organs:  earthworm  96;  frog 
12;  grasshopper  117,  118,  124; 
lobster  in,  107,  108;  Nereis  95; 
Planaria  go,  91 

Septa  98 

Serosa:  definition  of  7;  of  intestine 
34,  35 

Setae:  earthworm  97,  102,  103; 
Nereis  96 

Shank  3;  bones  of  55;  muscles  of 
60,  6 1 

Shell,  snail  136,  138 

Shrimps  125 

Sinus,  blood:  grasshopper  120,  121. 
122;  lobster  112,  113;  pericardia! 
^112;  sternal  113,  115 

Sinus  venosus  9,  45 

Siphonophora:  in  key  132;  in  text  88 

Skeleton:  breastbone  54;  definition 
of  5,  51;  endophragmal  115;  endo- 
skeleton,  definition  of  51;  exoskele- 
ton,  definition  of  51;  frog,  general 
5,  6;  frog,  special  51-55;  grass- 
hopper 117,  123;  hyoid  apparatus 
S3,  541  jaws,  frog  52,  53;  limbs, 
fr°g  55;  lobster  106,  115;  origin  of 
51,  67;  pectoral  girdle,  frog  54; 
pelvic  girdle  54,  55;  skull  51,  52-53; 
sternum  54;  vertebra,  parts  of 
51,  52;  vertebral  column  51,  52; 
visceral  skeleton  52-54 

Skin:  external  features  of  3;  histology 
of  36-37;  glands  of  36-37;  in 
respiration  19;  in  skeleton  51 

Skull:  bones  of  51-53;  definition  of  6; 
formation  of  52 

Small  intestine  9,  39;  histology  of 
26,  33-35 

Snail:  135-38;  behavior  135-36, 
food  ingestion  136-7;  radula 
136-37;  reaction  to  drying  137; 
reaction  to  lack  of  oxygen  137; 
reaction  to  light  137-38;  reproduc- 
tion 138;  respiration  137;  shell 
136-38;  structure  135-36 

Somite  95 

Sow  bugs  125 

Species,  definition  of  127 

Specific  name,  definition  of  127 

Spermatozoa:  definition  of  20;  earth- 
worm 101;  frog  32;  structure  of  32 

Spiders  125 

Spinal  cord,  frog:  cells  of  31,  38; 
function  of  14,  15,  49;  gross  struc- 
ture 12,  47,  48,  49;  histology  of  38 

Spinal  nerves:  frog  12,  47,  48,  49; 
roots  of  49 

Spindle  63 

Spiracles:  fly  21-22;  grasshopper 
119,  120,  121 

Spireme  63 

Spleen  10,  11 

Starch  test  18 

Starfish,  development  of  65-66 

Statocyst  in 

Stenlor  79 

Sternum:  frog  6,  54;  lobster  107; 
grasshopper  117,  119,  120 

Stigma  119.  120,  121 

Stinging  cells  82,  84 

Stomach:  frog  9,  39;  glands  of  35; 
grasshopper  123;  histology  of  35, 
36;  lobster  in,  114 

Styles  1 20 

Sub-esophageal  ganglion:  earthworm 
102;  grasshopper  123;  lobster  115 

Sugar  test  1 8 

Sulcus  marginalis  4 

Supra-esophageal  ganglion:  earth- 
worm 102;  grasshopper  124;  lobster 
"5 

Suture  117 

Swimmerets  108 

Syncytium,  definition  of  29 

Systemic  arch  44,  45 

Systems:  comparison  of  126;  of 
frog  8 


INDEX 


I49 


Fail  fan,  lobster  108 

Tapeworms:  in  key  132;  in  text  94 

Taxonomy,  definition  of  127 

Teeth:  frog  4;  lobster  114 

Telophase  63 

Telson  107 

Temperature,  effect  of,  on  activity  15 

Tendon  56;  of  Achilles  56 

Tentacles:    Hydra  82,  83,  84;   Nereis 

95;   snail  136 
Tergum  107,  117 
Testes:   earthworm  101;   frog  n,  40; 

function  of  20;    grasshopper  122; 

Hydra  86;  lobster  114 
Thalamencephalon  47 
Thigh,  3;    bones  of  55;    muscles  of 

59,  6p 
Thoracic    appendages:     grasshopper 

119;  lobster  108,  109 
Thorax:    grasshopper  117,  118,  xig; 

lobster  107,  no,  in 
Thyroid  gland  12 
Tissue,  definition  of  26 
Tissues:  connective  20-30;  epithelial 

27,  28;    frog  26-33;    muscular  28; 

nervous  31 

Tongue  4;  muscles  of  58,  59 
Tract,  definition  of  8 
Tracts  of  frog  8  . 

Tracheae.     See  Tracheal  tubes 
Tracheal  tubes:    fly  larvae   21,    22; 

grasshopper  119,  laz 


Transverse  processes  6,  51 
Trematodes:   in  key  132;   in  text  93 
Trichocysts  75,  77 
Triploblastic  71,  92 
Trochelminthes:     in    key    130;     in 

text  80 

Truncus  arteriosus  44,  46 
Trunk,  muscles  of  57 
Turbellaria:  in  key  132;  in  text  93 
Tympanic  membrane  2;  ring  57 
Typhlosole  100,  103 

Undulating  membrane  76 

Uniramous  appendage  108 

Unit  character  70 

Ureter  n,  40 

Urinary  bladder,  frog  8,  9,  40,  41,  10; 

ligaments  of  8,  10 
Urinogenital  system,  frog:    definition 

of  n;  general  10,  n;  special  40,  41 
Uropods  108 
Urostyle  6,  51 
Uterus  41 

Vacuoles:     contractile    72,    73,    76; 

food  73.  76,  77 
Variety,  definition  of  127 
Vasa  efferentia  40 
Vas  deferens:   earthworm  101; 

hopper  122;  lobster  114 
Vegetative  hemisphere  66 
Vein,  definition  of  9,  20 


Veins:  of  frog  5,  6,  42-43,  abdominal 
6,  43.  8,  hepatic  portal  43, 
musculo-cutaneous  5,  42,  pul- 
monary 43,  postcaval  42,  precaval 
42,  renal  portal  43,  systemic  42; 
of  wings  1 19 

Venous  system,  frog  42-43 

Ventricle  of  heart  9,  45,  46 

Ventricles  of  brain  46,  47,  48 

Vertebra,  structure  of  51 

Vertebral  column  6,  51,  52 

Vertebrata  in  key  131,  133,  134 

Vertebrates,  definition  of  72 

Vertex  117 

Viscera,  definition  of  5 

Visceral  skeleton  52,  53,  54 

Vocal  cords  41;  sacs 

Vomerine  teeth  4 

Vorticella  79 

Water  bears  81;  fleas  81;  mites  8 1 
Whitefish  eggs,  mitosis  in  64 
White  matter  of  cord  31,  38 
Wings  no 
Wolffian  duct,  xx 

Yolk  66 

Yolk  plug  66,  67 


Zooids  87-89 
Zygapophyses  51 


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